Can't launch the vast majority of non-steam games through Steam.
So if I add the exe as a non-steam game, then run with Proton (as I've done for years), clicking play will result in the game beginning to load, but it doesn't get anywhere, because before a load screen can show up, the play button switches back from "Stop" to "Play".
Through a Proton log created when launching these games, I can see that the game's launch, but Steam is force closing the application immediately.
Anyone else had this?