Proton 9 just got it's official release with a tonne of updates coming over from Proton Experimental and a lot more:
Previously playable only with Proton Experimental:
Alpha League
Battlezone Gold Edition in VR mode
Black Desert Online
FreestyleFootball R
Helldivers 2
Hero's Land
Iragon
SimCity 3000 Unlimited
Warlords Battlecry III
Enabled controller support for:
Clustertruck
Fallout 3 (standard and GOTY edition) - partial support only
Fallout 4
Mugsters
The Elder Scrolls V: Skyrim (original)
The Elder Scrolls V: Skyrim Special Edition
Tomb Raider: Anniversary
Tomb Raider: Legend
Limited number of cores seen by the following games making them playable on a high core count CPUs:
Call of Juarez: Gunslinger
Command & Conquer and The Covert Operations
Fixed Ghost of Tsushima and Horizon Forbidden West displaying a warning about outdated drivers with Nvidia GPUs.
Fixed The Finals crashing on launch after a recent game update.
Fixed The Finals wrongly detecting button mashing.
Fixed Apex Legends not starting after a recent game update.
Fixed Tekken 8 reporting wrong connection type if both WiFi and Ethernet are present.
Fixed Ubisoft Launcher not starting games with a fresh Proton prefix.
Fixed Halo Infinite crashing randomly during "initializing data".
Fixed Beat Saber not being playable on Nvidia GPUs without using the legacy branch.
Fixed Marvel vs Capcom: Infinite crashing when creating multiplayer lobby.
Fixed hosting multiplayer games in Foundry.
Fixed rendering of Japanese characters in the launcher of Granado Espada Japan.
Fixed Nightingale not being able to authenticate with Steam on desktop.
Fixed Bloons Monkey City thinking it's offline with IPv6 support disabled.
Fixed Ubisoft Launcher asking for serial number on the first launch of Tom Clancy's Ghost Recon: Future Soldier.
Fixed Descent 3 not working in GL mode.
Fixed Shatterline freezing on loading screen when trying to join a second online match in a session.
Fixed audio stutter in Viking: Battle for Asgard.
Fixed Russian language rendering in Brothers: A Tale of Two Sons launcher.
Fixed scaling in The Desolate Hope when playing on desktop.
Improved controller input support for Tower Princess.
Improved performance in We Love Katamari REROLL+ Royal Reverie.
Fixed GRIS showing error window when exiting the game.
Fixed issues with transparency in Akka Arrh.
Fixed load / save dialogs not working in Idle Spiral on Steam Deck.
Added raw HID support for VKB Gunfighter SCG.
Fixed random crashes in Cosmoteer Starship Architect & Commander.
Fixed font rendering in Cosmoteer Starship Architect & Commander on Steam Deck.
Improved Chinese font rendering in Cosmoteer Starship Architect & Commander.
Fixed Russian and Hebrew font rendering in Simon the Sorcerer: 25th Anniversary Edition.
Improved font rendering in Alien Swarm: Reactive Drop on Steam Deck.
Improved compatibility with OpenComposite.
You can check the full list of changes and follow the changes on GitHub here