Valve got Final Fantasy up and running on the Steam Deck after a Square Enix update to the launcher broke it earlier this year, and the latest release from the experimental launcher for Proton does this. So if that’s your MMO of choice, go ahead and upgrade to experimental and try it wherever you take your fancy portable PC.
Some other games are now playable on the experimental branch: Age of Chivalry, Chrono Cross: The Radical Dreamer Edition, Saviors of Sapphire Wings/Stranger of Sword City Revisited, Iragon: Prologue, One Piece: Pirate Warriors 4, Atelier Meruru, Warhammer : End Times – Vermintide, Star Wars Episode I Racer, Gary Grigsby’s War in the East, Gary Grigsby’s War in the West, Beneath a Steel Sky, We Were Here Forever, Cities XXL, Cladun X2, Succubus x Saint, Cursed Armor.
The update also has fixes for Elden Ring and DEATHLOOP crashes.
For my part, I’m absolutely shocked by the idea that Gary Grigsby’s War in the East and West works on the Steam Deck. I have no idea how you would play this…but now I have to try.