As I recall off the top of my head, gta5 (buggy), the division 2 (anticheat), the entirety of Forza Horizon 3+4 and Halo Wars 2 (since they are MS Store titles)… I want to say watch dogs legion (uplay) but tbh it’s been a bit and my memory is fuzzy. Also since proton is for steam, I assume EA/Origin, which wipes a dozen games with one swoop, too (modern NFS, The Sims, Burnout, Battlefield…).
I’ve got a bunch of older games too that I keep installed for nostalgia, but haven’t looked at their playability scores; stuff like (all listed are non-digital copies) NFS 2 through Most Wanted (2012), GTA 3 / VC / SA, Midtown Madness 1+2, System Protocol One, TDU 1+2 (with third-party multi-player support thru TDU World launcher)…
I think the rest of my currently installed games should work ootb (no mp/steam managed or GOG / physical copy/new enough that I don’t think they’d need patches or workarounds…). But with over 7k gameplay hours logged on the Forza Horizon series alone, there’s a lot I play daily and losing just a couple would be too much. I’m out of the ‘tinker until it works’ phase, I just want things to work, ya know?
Edit: I’m also not sure how deeply ingrained the MS account stuff is, but also Horizon 5 (steam) and Halo MCC + Infinite (steam) too