Some proton versions are compatible with some games, or some versions of games. Use whatever works, but generally, the newer the Proton version, the better performance you'll get out of a game. Check for compatibility notes and tricks per game here: https://www.protondb.com/

Evolution is fine. Thunderbird is fine. There's a bunch of others as well. Use whatever you like!

I installed GE proton, which fixed the lobby audio bug in phasmophobia, is there any reason I shouldn't just use that version of proton for all steam games?

Typically if you install a specific version to fix a specific bug, that version will be static (to maintain the bugfix) and may not get future Proton updates rolled into it (unless someone is actively maintaining that special version).

It's best to stick with the default Proton version (which should be the latest stable build) except when you need to fix a specific problem, and assign specific fix versions only for the game/application that requires it.

Evolution is a fine mail client, but I'm not too sure if it's being actively developed much. Not many distros ship it out of the box.

If it works, it's fine to use GE builds, but generally I just leave it on the default for Steam and only change it if I have a problem.

The reason is, different proton builds work better or worse for different games depending on the optimizations in that particular build and game. GE is pretty solid all around, but with some older games you may need to roll back or go to experimental for some others

I like Evolution too

I liked the UI of Evolution when I used it, but there were some usability issues which made me switch to Thunderbird in the end. There's a good extension in Thunderbird for markdown support when composing emails, which I could not use on Evolution. And Evolution failed to attach .eml files when I tried that (as opposed to including previous emails inline). But if your email use case is very basic, it should be fine.