Here's a method to run an AppImage on Pop!_OS that worked for me.
An AppImage is a file that contains a Linux that will supposedly "run anywhere". It probably does, who knows. But for me, I had trouble with running one that I tried recently.
Looking for help, I found some that suggested using
fuse to run a file. But I got stuck on
apt install dependencies, so I looked for alternatives.
The simplest of all was to run the AppImage with a flag,
--disable-gpu-sandbox. And that worked! The app started up, and here's the full, simple solution:
chmod a+x Polypane-16.0.0.AppImage ./Polypane-16.0.0.AppImage --disable-gpu-sandbox
Why does this work? I don't know. It's probably because this app has some embedded Firefox in it. But maybe there's a more generalized reason. If you have insight, I'd love to hear it.