Oh wow, I haven’t heard about Sandboxie in a long while. I tried using it years ago, but I didn’t understand the documentation and gave up. Maybe I should try it out again sometime.

I personally like flatpaks, but sometimes even with Flatseal it’s hard to figure out which permissions are needed for things to work. (For example, I tried making flatpak Calibre open PDFs using another flatpak program, but I never got that working.)