Having a little trouble getting rolled back to the older version...what I'm actually doing right now is running the older version through the AppImage package; the version actually installed on my system is still 5.3. But instead I removed the entire .local/share/cura directory to clear any existing profiles, which seemed to work as it took me through the initial setup wizard and make me configure a new printer (and there's no previous configurations shown), I set up the printer as the UM 3S, but I still can't open or save anything (in fact, when I click 'Save Project' from the file menu the entire program locks up and has to be forcibly killed.)
I did also try the AppImage version of 5.3 (linux-modern; the other doesn't run on my system), but have the same issue with that.
Tried a few other versions on the AppImages too:
4.13 works
5.0 won't launch due to OpenGL 2.0 issue (on my Intel gpu) or gtk2 issue (using prime-run to run on my Nvidia gpu)
5.1 to 5.2 fail with gtk2 issue (on either gpu, using linux-modern package)
5.2.1 or greater runs but can't open or save anything (on either gpu, using linux-modern package).
cura.log