apt can't install anything after manually upgrading kernel to 5.18

Question

I got a new laptop for work and now destroyed it lol I installed Debian 11 with LVM and everything I needed.

How I ended up in this situation

Everything was perfect, except for my docking station setup. Very long story short: I tried seemingly everything, but I couldn't get the DisplayLink setup to work with my laptop and two external monitors, even though my co-worker could, using the same exact hardware. I had one screen only having interlaced as the highest resolution and I found out, that DisplayLink shouldn't be necessary at all anymore, so I tried upgrading to Kernel version 5.18.0-3-amd64, because I read it has more support in these fields. I followed this guide. It didn't get my third monitor to work, but now I could use the highest resolution without interlaced. That was good enough for me.

Though, I noticed whenever I wanted to install something with apt, it caused some issues. I just tried to uncomment the Debian unstable sources and it would work lol

But now? apt tried to uninstall a LOT. It wanted to remove half a giga byte. I googled, found out it shouldn't be, looked a bit through and among it was gnome and other essential stuff. I aborted ofc and figured it's the kernel upgrade (since the newest supplied from debian was 5.10.0-16-amd64)

I tried to find a guide to downgrade. I ran "apt install --fix-broken", rebooted into the old kernel that was still installed and I found myself in a console, not a desktop environment. All of theses packages got uninstalled :) Now I can't install anything, not even with dpkg. Could dpkg's database be broken?

Also: I installed linux-headers-5.18.0-3-common_5.18.14-1_all.deb and all its dependencies manually with dpkg, because they were necessary for VirtualBox and I couldn't get it to work with apt whatsoever, so I just tried this and it worked. I don't know if that could interfere somehow.

The error

I searched, tried, etc. but absolutely no clue what to do now. Anything I try in terms of installing/upgrading results in this:

The following packages have unmet dependencies:
 libtext-charwidth-perl: Depends: perlapi-5.34.0 but it is not installable
 libtext-iconv-perl: Depends: perlapi-5.34.0 but it is not installable
 perl: Breaks: perl-modules-5.24 but 5.24.1-3+deb9u7 is installed
E: Unmet dependencies. Try 'apt --fix-broken install' with no packages (or specify a solution).

I honestly don't even get what that's supposed to mean. The more I research, the more I get confused. I don't even know what to Google at this point.

What I tried

downgrading. I think that's what I have to do, but idk how. I looked for something that downgrades all packages into an installable version (e.g. to Debian 11 released standards), but couldn't find anything close to it. I can only find tutorials that all say "package=version". I googled the packages and perlapi is a virtual package that comes from perl-base, so I tried to install the version 5.34.0 via apt and also via wget of https://packages.debian.org/sid/amd64/perl-base/download and dpkg -i

But apt says:

E: Version '5.34.0' for 'perl-base' was not found

I mean... it said it couldn't install it, but some forum solutions said to just manually install it. I don't even know why it wants this version to begin with. I am using kernel 5.10 with standard apt sources (tried everything with added and removed extra sources):

deb http://packages.hs-regensburg.de/debian/ bullseye main contrib non-free
deb-src http://packages.hs-regensburg.de/debian/ bullseye main contrib non-free

deb http://security.debian.org/debian-security bullseye-security main contrib non-free
deb-src http://security.debian.org/debian-security bullseye-security main contrib non-free

deb http://deb.debian.org/debian unstable main contrib non-free
deb-src http://deb.debian.org/debian unstable main contrib non-free

And dpkg says:

dpkg: regarding perl-base_5.34.0-5_amd64.deb containing perl-base:
 perl-base breaks libfile-spec-perl (<< 3.8000)
  perl provides libfile-spec-perl and is present and installed.

dpkg: error processing archive perl-base_5.34.0-5_amd64.deb (--install):
 instaling perl-base would break perl, and
 deconfiguration is not permitted (--auto-deconfigure might help)
Errors were encountered while processing:
 perl-base_5.34.0-5_amd64.deb

--auto-deconfigure didn't help

I'm not sure anymore what even the problem is at this point. I am utterly lost. Please help <:C Please keep in mind, that I can't install anything and "re-installing Debian" is not an option. I didn't all the time to just do it again. If you need anything, ask and I'll try to provide

Update

I managed to send text via SSH and putty on Windows (typed everything before).

Here is additional information: https://pastebin.com/XNKLMRkB

Update 2

I came up with this unfinished apt command, trying to resolve these dependency issues:

apt install libtext-charwidth-perl=0.04-10+b1 perl-base=5.32.1-4+deb11u2 libtext-iconv-perl=1.7-7+b1 perl=5.32.1-4+deb11u2 perl-modules-5.32=5.32.1-4+deb11u2

This is what I get:

Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
perl is already the newest version (5.32.1-4+deb11u2).
perl-modules-5.32 is already the newest version (5.32.1-4+deb11u2).
perl-modules-5.32 set to manually installed.
You might want to run 'apt --fix-broken install' to correct these.
The following packages have unmet dependencies:
 perl : Breaks: perl-modules-5.24 but 5.24.1-3+deb9u7 is to be installed
E: Unmet dependencies. Try 'apt --fix-broken install' with no packages (or specify a solution).

It somehow thinks it needs 5.24 from Debian 9 (like Stephen Kitt already pointed out. Thank you). I tried to simply use the newer version, block this version, make it negative priority, uninstall or somehow bypass it. Nothing worked :C I guess I'm one step behind. I Just need to know how to step forward.

dpkg error when tryin to uninstall:

dpkg: dependency problems prevent removal of perl-modules-5.24:
 libmailtools-perl depends on libnet-perl; however:
  Package libnet-perl is not installed.
  Package perl-modules-5.24 which provides libnet-perl is to be removed.
  Package perl which provides libnet-perl is not configured yet.
 libmailtools-perl depends on libtest-simple-perl; however:
  Package libtest-simple-perl is not installed.
  Package perl-modules-5.24 which provides libtest-simple-perl is to be removed.
  Package perl which provides libtest-simple-perl is not configured yet.
 libmailtools-perl depends on libnet-perl; however:
  Package libnet-perl is not installed.
  Package perl-modules-5.24 which provides libnet-perl is to be removed.
  Package perl which provides libnet-perl is not configured yet.
 libmailtools-perl depends on libtest-simple-perl; however:
  Package libtest-simple-perl is not installed.
  Package perl-modules-5.24 which provides libtest-simple-perl is to be removed.
  Package perl which provides libtest-simple-perl is not configured yet.
 libhttp-date-perl depends on libtime-local-perl (>= 1.28); however:
  Package libtime-local-perl is not installed.
  Package perl-modules-5.24 which provides libtime-local-perl is to be removed.
  Package perl which provides libtime-local-perl is not configured yet.

dpkg: error processing package perl-modules-5.24 (--remove):
 dependency problems - not removing
Errors were encountered while processing:
 perl-modules-5.24

When I try to configure all missing packages:

dpkg: dependency problems prevent configuration of perl:
 perl depends on perl-base (= 5.32.1-4+deb11u2); however:
  Version of perl-base on system is 5.34.0-5.
 perl-base (5.34.0-5) breaks perl (<< 5.34.0~) and is installed.
  Version of perl to be configured is 5.32.1-4+deb11u2.

dpkg: error processing package perl (--configure):
 dependency problems - leaving unconfigured
Errors were encountered while processing:
 perl

Answer 1

I managed to clear things up.

Like suggested in a bunch of different forums, I had to manually downgrade the packages (like I anticipated), by specifying the specific version. Luckily, in this case, it wasn't too many.
But one package still made problems: perl-modules-5.24

apt and dpgk refused to upgrade and even remove any packages, because of these. perl-modules-5.24 actually belongs to Debian 9 So it was safe to remove, but it wouldn't let me.
I couldn't downgrade because of it and I couldn't upgrade because of it.
I was stuck in a loop, but thankfully, I could force dpkg.

This is how I managed to resolve it:

First step: Pray
Next steps: With the help of this answer, I managed to uninstall that stupid package:

dpkg -r --force-depends perl-modules-5.24

I made sure my /etc/apt/sources.list was correct:

deb http://packages.hs-regensburg.de/debian/ bullseye main
deb-src http://packages.hs-regensburg.de/debian/ bullseye main

deb http://security.debian.org/debian-security bullseye-security main
deb-src http://security.debian.org/debian-security bullseye-security main

# bullseye-updates, to get updates before a point release is made;
# see https://www.debian.org/doc/manuals/debian-reference/ch02.en.html#_updates_and_backports
deb http://packages.hs-regensburg.de/debian/ bullseye-updates main
deb-src http://packages.hs-regensburg.de/debian/ bullseye-updates main

Then I could install:

apt install libtext-charwidth-perl=0.04-10+b1 perl-base=5.32.1-4+deb11u2 libtext-iconv-perl=1.7-7+b1 perl=5.32.1-4+deb11u2 perl-modules-5.32=5.32.1-4+deb11u2

(I didn't exactly need all of these packages, as I was already informed before, that some of these are already installed at these versions, but at this stage, I just made sure)
And through my backup list of uninstalled packages, installed them back again:

apt install $(cat apt-autoremove-list | awk 'BEGIN {ORS=" "}; {for(i=0;i<=NF;i++){print $i}}')

Luckily, apt and dpkg now aren't crying about a damn debian 9 package anymore. Idk what got caught them up in that...

And I could reboot back into my desktop environment... "my"
I had to install gnome back, but some packages had problems again.
This time, they didn't "break" tho, they simply still had the "too new" packages from unstable. So I resolved these by manually installing the correct version:

apt policy <package>
apt install <package>=<stable version>

And while installing gnome back via the Putty session, it jumped right into it on my laptop after installation.
Hoory. Finally, after 8 hours, some sleep. It took me days to configure everything. Worth it. :)

Thank you all for your contribution and quick responses!

Edit:

I wrote a script that tries to install the latest versions of the packages. It may need to be adjusted in the future, but it does its job.

#!/bin/bash

installations=$(apt list --installed)
i="null"
packagesToInstall="";


# changable variables (don't change the ones above here)
debug=0

echo "Notice: Analyze this script's doings first, before you install anything, as apt still claims their CLI interface is not stable"
echo -e "\tAdjust this script if something goes wrong!!!\n\n"

getPackage() {
    parray=(${1//// }) # replace slashes with spaces to convert it into an array

    echo "${parray[0]}"
}

echo "collecting packages to install..."

for attribute in $installations; do
    # skip "Listing... Done"
    if [ "$i" == "null" ]; then
           i=0
           continue
    fi       

    i=$(($i + 1))

    # apt's output pattern upon developing this script:
    #
    # zlib1g-dev/stable,stable-security,now
    # 1:1.2.11.dfsg-2+deb11u1
    # amd64
    # [installed]
    # zlib1g/stable,stable-security,now
    # 1:1.2.11.dfsg-2+deb11u1
    # amd64
    # [installed]


    case "$i" in
        "1")
            package=$(getPackage "$attribute")
            ;;
        "2")
            oldVersion=$attribute
            ;;
        "3")
            architecture=$attribute
            ;;
        "4")
            status=$attribute
            ;;
        "5")
            i=1
            unset "newVersion"
            unset "correctVersion"
            unset "correctVersions"


            # get correct version

            # https://serverfault.com/questions/1073939/debian-11-security-updates-deb-or-security-which-to-choose
            # https://www.linuxheld.de/2021/11/08/upgrade-debian-buster-10-auf-debian-bullseye-11/
            correctVersions=$(apt policy "$package" 2>/dev/null | grep " $(lsb_release -cs)/" -B 1)
            correctVersion=$(echo "$correctVersions" | awk '{print $1}')

            # if a version was found
            if [[ "$correctVersion" != "*"* ]]; then
                #echo "?$correctVersion?"
                correctVersion=($correctVersion) # toArray
                #echo "!$correctVersion!"
                newVersion=${correctVersion[0]}
            fi

            
            if [ "$debug" == 1 ]; then
                echo "package: $package"
                echo "installed version: $oldVersion"
                echo "architecture: $architecture"
                echo "status: $status"
                echo -e "new version: $newVersion\n"
                #echo "$correctVersions"
            fi




            # do actions (install)

            # if there is a new version available to install
            if ! [ -z "$newVersion" ] && [ "$oldVersion" != "$newVersion" ]; then
                packagesToInstall="$packagesToInstall"' '"'$package=$newVersion'"
            fi

            # continue
            package=$(getPackage "$attribute") # 1 from case statement only gets executed the first time
            unset "oldVersion"
            unset "newVersion"
            unset "correctVersion"
            unset "correctVersions"
            continue
            ;;
    esac
    #echo $install | awk '{print $2}'
done

echo -e "installing following packages with versions:\n"

for pti in $packagesToInstall; do
    parray=(${pti//=/ })

    if [ -z "$parray" ]; then
        echo "$pti"
    else
        package="${parray[0]}"
        version="${parray[1]}"

        package=${package#*"'"}
        version=${version%"'"*}

        printf "$package:\t"

        if [ "${#package}" -lt 7 ]; then
            printf "\t\t\t\t"
        elif [ "${#package}" -lt 15 ]; then
            printf "\t\t\t"
        elif [ "${#package}" -lt 23 ]; then
            printf "\t\t"
        elif [ "${#package}" -lt 31 ]; then
            printf "\t"
        fi

        echo "$version"
    fi
done

echo ""
read -p "Install all of these? [Y/n] " userWantsToInstall
userWantsToInstall=${userWantsToInstall,,} # https://stackoverflow.com/questions/1728683/case-insensitive-comparison-of-strings-in-shell-script

# ask before installation
if [ "$userWantsToInstall" == "y" ] || [ -z "$userWantsToInstall" ] || [ "$userWantsToInstall" == "yes" ]; then
    if [ $(whoami) == "root" ]; then
        echo "apt install --yes --force-yes $packagesToInstall"
    else
        echo "sudo apt install --yes --force-yes $packagesToInstall"
    fi
else
    echo -e "\nAborted"
    exit
fi