I'm far from an expert but I believe Proton is specifically intended to provide compatability with Windows gaming tech like DirectX.

For regular non-game software you don't need that tech, you can just run it through Wine itself (Proton is built on Wine). Bottles is actually what I see recommended these days (it simplifies management of Wine prefixes) and supposedly many apps can run in a few clicks.

Not strictly proton, but for wine, you can see here (https://appdb.winehq.org/) that it supports more than just games.

Lots, but if they interface with usb (like an image writer or mouse software) it won't work.

I'm pretty sure there are wine builds with all the proton enhancements that aren't in normal wine yet. I feel like I saw in lutris or bottles or both but you can surely get it other ways too.

On top off my head is the old non UWP version of Photoscape which I use from time to time to do basic edits.

Then Finale notepad for music transcribing stuff

I use to use MSOffice 2007 but recently I have switched to OnlyOffice

Although most of them, or atleast what I know off, are made for older version of windows

Notpad++ works in Wine. And I used to run JMP 10 with wine too (data plotting software). Neither required Proton though.

I dunno about Proton but I'd assume do. I have some CAD and 3D software I use in Wine.