Destiny 2 and COD have kernel anticheat which is what I was referring to. I doubt Starfield will have that, as it would go against everything Bethesda has stood for in the past with modding. Apex Legends is listed as Gold in proton DB, it looks like it runs fine. Forza Horizon 5 is silver in protonDB, it looks like it is playable with a little bit of tweaking. Far Cry 6 is Gold in protonDB, it looks like it runs fine.
Plus, Apex Legends and Destiny 2 aren’t new. I was referring to games that came out in the last two years, after the Steam Deck came out. Destiny 2 came out 6 years ago.
At this point, unless there’s kernel anticheat pretty much everything is playable. So that’s going to rule out many competitive games, which you specifically called out, but since the game in question is a single player game, I think it will be fine.