GloriousEggroll has released an updated custom build of their 5.9 Proton fork.

Proton-5.9-GE-3-ST

After ironing out a lot of the major bugs since 5.11, I've realized that while some games run well enough without esync/fsync, the majority of games, specifically triple A titles, really need esync/fsync, especially when running on lower end hardware.

SO, what I've done is taken -all- of the fixes from the 5.11 versions and upstream that are major/relevant that I could recall, and backported them to the 5.9 build. This returns esync/fsync functionality, and also enables some games to run correctly that weren't running in 5.11.

So yes, this is aimed as a 'STABLE' build.
-All the fixes from the 5.11 releases.
-esync/fsync re-enabled
-MGS: Ground Zeroes fully works
-Planet Zoo fully works

From here I've created yet another branch -- proton-ge-5-stable, which I hope to backport future fixes to, and bump up once Wine gets all of its current kinks resolved. The proton-ge-5-MF branch will continue to be the upstream git branch, with major game fixes being backported to the stable branch (hopefully).

Download Proton 5.9-GE-3-ST from GitHub
Installation Instructions