Introduction
Recently I accomplished a brand new installation of PopOS 20.10 standard image (not NVIDIA one).
I have Intel UHD Graphics 620 (rev. 7) / i7-8650U installed.
Problem statement
I noticed a very laggy UI, just the same way when you don't have Intel graphics drivers installed on your Windows machine.
I.e. when you view animations while surfing the web in your browser.
Solution
Just move to Wayland from X11 and that should resolve the issue for 100% (that did for me).
Guideline
# Edit GDM3 configuration
# set (or add this entry if missing) WaylandEnable=true
sudo nano /etc/gdm3/custom.conf
# Restart the GDM3 daemon
sudo systemctl restart gdm3
Now you should see PopOS on Wayland on the login screen under gear button. Choose that option.

Check which display protocol is being used
echo $XDG_SESSION_TYPE