I do not see one (does not mean it is not there). When I used to watch this project more closely you had to just goto the game db and hope someone tested it. You can also look through the commit logs and usually the reference the specific application they are fixing. The rc bits usually have the bugfixes and those too have which app that bug has fixed. They have a ranking of how good the game is. So there may have been a bug fixed but it is still broke because of 10 other things.
Protondb.com is a fantastic place to see if a game is supported on Steam through Proton. Since it's all open source, proton can also be used outside of steam.
