You can pick source code from any release: https://github.com/ValveSoftware/Proton/releases and compile it yourself. It's a pity Valve doesn't publish there precompiled binary.
Maybe you can also download old version with command depot_download like described here: https://steamcommunity.com/sharedfiles/filedetails/?id=889624474 , but I don't know.
proton 5.0x1 2020-06
I think I'm running into issues with proton 5.0.8, I couldn't find an issue about this and since #3932 was closed I figured it's probably best to create a new issue.
Is there a way to use the previous minor/patch version of Proton? Or any version for that matter? I can only select previous major versions in the Steam UI.
Asking because I think I'm experiencing worse performance in a game than I was getting on 5.0.7 but I can't compare because I'm unable to run that version at the moment.