A couple of days ago, Valve has released the first stable version of Proton 9.0, a compatibility layer for Windows games to run on Linux-based operating systems. The newest stable version is built on Wine 9.0 and brings all the improvements and fixes seen in earlier beta releases.

According to the release notes, the new Proton 9.0-1 enables some games that were previously playable only with Proton Experimental, including Sonic Colors: Ultimate, Command & Conquer games, The Finals, Lord of the Rings: Gollum and others, enables NVIDIA NVAPI by default for most games, adds support for Steamworks SDK 1.59, and fixes a bunch of other issues in a lot of games. The new version also limits the number of cores seen by some games in order to make them actually playable on CPUs with high core count, including Far Cry 2 and Far Cry 4, The Witcher 2: Assassins of Kings Enhanced Edition, a couple of Warhammer 40,000 games and others.The new Proton 9.0 can be found in the Steam Library and those already running the beta version of Proton 9.0 should get it automatically.

Here are the full release notes from Github.

Changelog - Proton 9.0-1

• Previously playable only with Proton Experimental:
  • Dinogen Online
  • Photography Simulator Demo
  • George McGeehan Gamer Hero
  • The Finals
  • True Reporter. Mystery of Mistwood
  • Road to Vostok Demo
  • WITCH ON THE HOLY NIGHT
  • Lord of the Rings: Gollum
  • Sonic Colors: Ultimate
  • Command & Conquer: Red Alert 2 and Yuri's Revenge
  • Command & Conquer Tiberian Sun and Firestorm
  • Aisling and the Tavern of Elves
  • Snares of Ruin 2
  • Insanity's Blade
  • Bloody Walls
• Limited number of cores seen by the following games making them playable on a high core count CPUs:
  • Far Cry 2
  • Far Cry 4
  • The Witcher 2: Assassins of Kings Enhanced Edition
  • Lara Croft and the Guardian of Light
  • Warhammer 40,000: Space Marine
  • Warhammer 40,000: Dawn of War II
  • Warhammer 40,000: Dawn of War II - Chaos Rising
  • Warhammer 40,000: Dawn of War II - Retribution
  • Outcast - Second Contact
  • Prototype
• Enabled nvapi by default for most games.
• Started ignoring system mouse acceleration in games using raw input API.
• Fixed Brawhalla showing a security certificate warning.
• Fixed audio in BOOMEROAD, DORONKO WANKO, NOTTOLOT.
• Fixed Civilization V Touch Only option in the launcher not working.
• Improved cutscene synchronization in Immortals Fenyx Rising.
• Fixed TouHou Makuka Sai ~ Fantastic Danmaku Festival Part I and II crashing during boss fights.
• Fixed crash in Disaster Report 4: Summer Memories epilogue.
• Improved video playback in BIOMUTANT.
• Fixed Imperiums: Greek Wars launcher.
• Fixed memory leaks that caused Final Fantasy XIV Online launcher crash over long time.
• Fixed crash in Microsoft Flight Simulator when live weather is enabled.
• Improved support for input devices with 8+ axes.
• Fixed Savant - Ascent REMIX hitching during certain animations.
• Fixed Super Robot Wars 30 crashing with languages other than English.
• Fixed Doom Eternal audio crackling on certain setups.
• Fixed Lethal Company, Phasmophobia and other Unity games crashing when a controller with a hat switch is plugged in.
• Improved video playback for the following titles: Lords of the Fallen, Harvestella, Wayfinder, Sea of Thieves, and KING OF FIGHTERS XV.
• Fixed default scaling for The Last Game on Steam Deck.
• Fixed audio issues when playing intro video in Airborne Kingdom.
• Fixed Bayonetta crashing on certain systems.
• Fixed Escape from Monkey Island getting minimized on a mouse click.
• Fixed audio controls and spatialization in VRChat with AVPro.
• Fixed new prefix failing to initialize on filesystem that do not support copy_file_range syscall.
• Updated file distribution method to save disk space.
• Rebased on top of upstream Wine 9.0.
• Updated vkd3d-proton to v2.11.1-49-g32ff676b.
• Updated dxvk to v2.3-47-ge2a46a34.
• Updated dxvk-nvapi to v0.6.4-48-g0951afb.
• Added support for Steamworks SDK 1.59.