Games sometimes have wildly different behaviors based on the version of Proton used.
(eg.: starting VR games on proton 8 with the new SteamVR v2.14 crashes my whole mesa driver, while proton 9 works fine)

I keep a .txt file to log my experiences, to know which one to set.

The compatibility window has a lot of empty space, which could be used for a Notes section, similar to the one you've added to the Steam Overlay a few years back. Users could track their experiences very conveniently there.