But a recent upgrade gave me a problem. I started the app and the windows were missing their borders and my mouse cursor was too small.

Not show-stopping problems, but mildly annoying. After a bit of faffing around, I discovered the cause and how to fix it.

I was running the Flatpak version of Calibre. Normally I find Flatpaks work really well, but it seems that this particular one had an issue with the Wayland display system used by Pop OS and other modern Linux distros.

The fix was pretty easy. I installed Flatseal which is an app to manage the settings of Flatpaks. Then I told Calibre that it shouldn't use Wayland and should instead fallback to the older X11 display.

And, with that, everything looked as it should again:

I think Wayland is a pretty snazzy bit of software, but it's new so there are going to be teething problems. Luckily, this was a fairly straightforward fix.

Edit this file:

sudo nano /etc/gdm3/custom.conf

Find this line:

WaylandEnable=false

Change it to:

#WaylandEnable=false

Reboot.

On Pop!_OS, there is this settings cog in the bottom right corner. (Different login screens may have it elsewhere).

Choose "Pop on Wayland". Or "Wayland" - depending on your Desktop Environment.

That's it! No tearing when scrolling or playing videos! If you've changed your screen scaling, you might have to fiddle with it to get back to normal - but everything should just work.