Valve has just updated this October the whitelist for Windows Games that work (flawlessly?) using Proton. Such games should appear just like Linux native clients in your library in case you did not allow Steam Play to accept all title:

• AdVenture Communist
• Aftergrinder
• Bejeweled 3
• Castle Crashers
• Cat Goes Fishing
• Coffee Shop Tycoon
• Coloring Pixels
• Commander Keen Complete Pack
• Everyday Shooter
• Fieldrunners 2
• Guacamelee 2
  
• Heretic: Shadow of the Serpent Riders
• HeXen: Beyond Heretic
• HeXen: Deathkings of the Dark Citadel
• Mighty Switch Force! Hyper Drive Edition
• Monkey Island 2 Special Edition: LeChuck’s Revenge
• Overcooked
• Puzzle Agent
• Sam & Max Season 1
  
• Sam & Max Season 2
• Sam & Max Season 3
• Spelunky
• Stick Fight: The Game
• VirtuaCreature
• The Witness
• Wolfenstein: The Old Blood
  
• Zen of Sudoku

A lot of older titles in this list (Monkey Island 2 Special Edition is just a HD version of the old game), or Telltales games (RIP) like the newer Sam and Max series. But the most interesting additions in this list are The Witness (from Jonathan Blow who used to say that Linux can’t reliably draw 3D) and Wolfenstein: the Old Blood, a prequel to the Wolfenstein universe, published by Bethesda. My guess is that the new Wolfenstein will also be whitelisted at some point since it uses Vulkan as the only graphics API so it’s probably a low hanging fruit as well. Also worth nothing that Guacamelee 2 now works on Linux with Steam Play: in case you liked the first episode and wanted more, now is the time to consider getting it on Linux!