I also wrote my own Python based installer, updater, manager of Proton GE (but do not post it here, as this is about your project and not mine). Years back when I posted it, people pointed out such a cli tool already existed: protonup. And for those who want a GUI, protonup-qt exists too.

rm -r $tempdir

This is extremely dangerous command! If anything goes wrong for whatever reason and the variable $tempdir is empty at the time of this command, then it would delete everything. At the very least you should do a check if variable is not empty and resolves to an existing directory. Better yet, make it multiple steps:

1. check if variable is not empty
2. check if variable resolves to a directory
3. cd into the directory and delete content by name instead a variable, like rm -r GE-Proton* and then cd .. back and delete empty directory with rmdir $tempdir

This is a more controlled way of deleting files. I admit that I am a bit paranoid with rm -r commands.