I tried to run Tor Browser, installed from the Ubuntu 20.04 official repository. First the browser just wouldn't start:
$ torbrowser-launcher
Tor Browser Launcher
By Micah Lee, licensed under MIT
version 0.3.2
https://github.com/micahflee/torbrowser-launcher
Your version of Tor Browser is out-of-date. Downloading the newest version.
Downloading https://aus1.torproject.org/torbrowser/update_3/release/Linux_x86_64-gcc3/x/en-US
$ echo $?
0
Then I tried to open the Tor Browser settings to see if there was anything I could do. I tried "Reinstall Tor Browser" and got this output:
$ torbrowser-launcher --settings
Tor Browser Launcher
By Micah Lee, licensed under MIT
version 0.3.2
https://github.com/micahflee/torbrowser-launcher
Downloading Tor Browser for the first time.
Downloading https://aus1.torproject.org/torbrowser/update_3/release/Linux_x86_64-gcc3/x/en-US
Latest version: 10.0
Downloading https://dist.torproject.org/torbrowser/10.0/tor-browser-linux64-10.0_en-US.tar.xz.asc
Downloading https://dist.torproject.org/torbrowser/10.0/tor-browser-linux64-10.0_en-US.tar.xz
Verifying Signature
Refreshing local keyring...
Traceback (most recent call last):
File "/usr/lib/python3/dist-packages/torbrowser_launcher/launcher.py", line 589, in verify
c.verify(signature=sig, signed_data=signed)
File "/usr/lib/python3/dist-packages/gpg/core.py", line 541, in verify
raise errors.BadSignatures(results[1], results=results)
gpg.errors.BadSignatures: 110775B5D101FB36BC6C911BEB774491D9FF06E2: Key expired
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "/usr/lib/python3/dist-packages/torbrowser_launcher/launcher.py", line 600, in run
verify()
File "/usr/lib/python3/dist-packages/torbrowser_launcher/launcher.py", line 594, in verify
raise Exception
Exception
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "/usr/lib/python3/dist-packages/torbrowser_launcher/launcher.py", line 603, in run
self.common.refresh_keyring()
File "/usr/lib/python3/dist-packages/torbrowser_launcher/common.py", line 196, in refresh_keyring
p = subprocess.Popen(['/usr/bin/gpg2', '--status-fd', '2',
File "/usr/lib/python3.8/subprocess.py", line 854, in __init__
self._execute_child(args, executable, preexec_fn, close_fds,
File "/usr/lib/python3.8/subprocess.py", line 1702, in _execute_child
raise child_exception_type(errno_num, err_msg, err_filename)
FileNotFoundError: [Errno 2] No such file or directory: '/usr/bin/gpg2'
I solved the missing /usr/bin/gpg2 with sudo apt install gnupg2. Several posts suggest to run gpg --homedir "$HOME/.local/share/torbrowser/gnupg_homedir/" --refresh-keys to refresh the keys, but I still kept getting the same error message about the expired key. Looking at the Tor Browser documentation I first tried gpg --auto-key-locate nodefault,wkd --locate-keys [email protected] and got the same result, then gpg --homedir "$HOME/.local/share/torbrowser/gnupg_homedir/" --auto-key-locate nodefault,wkd --locate-keys [email protected].
At this point, trying to upgrade via torbrowser-launcher --settings results first in an error message:
The version of Tor Browser you have installed is earlier than it should be, which could be a sign of an attack!
which seems to be a known issue and then the installer gets stuck: 
Workaround: Run ~/.local/share/torbrowser/tbb/x86_64/tor-browser_en-US/Browser/start-tor-browser to start the new Tor Browser 10 directly.
