Steam Deck and UE4 (UE5) a guide... (?)

Has anyone managed to run a compiled UE5 project?
I tried GonziHere’s method (package for win64, copy to steam deck, on deck desktop add it to steamOS, switch to steamOS, launch project using various versions of Proton) and all I get is the animated steam logo looping forever, the game never starts.

I see the same behavior with some commercial games that I know will run on steam deck but aren’t from the Steam store, so I hope maybe there is just some steam deck trick to launching a non-steam game in steamOS that I might be missing…?