Trrereeee: I'm using gog galaxy launcher. But I can only launch it in desktop mode. But I launch it in steam so hopefully the proton I use to start gog galaxy also uses that same proton to run the game. If this doesnt work I will try to add the game directly to steam from heroic again I figured out how to do ot but I have to re download the game in heroic then set up the correct paths. Wish me luck since I'm not computer knowledgeable
Great that you got it working :)
Anyway, I don't use Galaxy or Heroic at all, just download the offline installer from the GOG website. It's a bit tricky to install the games manually but worth it to have zero clutter on the already limited Steam Deck. Maybe worth considering in the future if you don't install a lot of games at the same time.