After a couple of months where Proton seemed to decline in terms of overall compatibility (some of it explained by regressions, others by newer Windows games not running as well as other games relatively speaking). it looks like Proton is back is business in September:

It does not look the best yet if you focus only on the Gold/Platinum ratings, but the number of Borked games (i.e. games not running at all even with user attempts to fix things) is back to what it was in June this year. This is what I expected after contacting Codeweavers last month about the trend.

I was just looking at the top 30 new games reported upon by users in September as well, and the number of borked games there was just 6/30 - which matches the 20% ratio you see on this graph pretty closely.

Games that stopped working such as GTA V are also being worked on, as proven by a recent Proton release notes (4.11-6):

The Surge 2 is now playable (currently doesn’t work on radv).Beginnings of support for Rockstar’s new launcher. There is more work to do here, but Grand Theft Auto 5 should be playable again.Update DXVK to v1.4.

Next I will cover the list of newly compatibles games running with Proton in September 2019, at least in terms of popularity. Stay tuned!