If it helps I played AC Odyssey w/o issues using Proton GE, the biggest issue for me was that when I launched the game through steam, steam would launch the Ubisoft launcher which then launched the game , so I had to manually close this launcher to prevent having proton running in the bg for too long
It's been a while since I gamed though (2022), but the game ran smoothly on a mobile RTX 2060 card
The launcher is a bit annoying at times but what finally made me commit ot the switch was when I realized that Anno 1800 and the demo for Anno 117 were running flawlessly.
I also recently finished AC Origins for the first time on my Linux machine.
However I don't play multiplayer ever and apparently that's where most issues are.
Was the demo through Steam or through Ubisoft Connect launcher?
I'm a huge Anno fan and I play Anno 1800 like all the time. I own that game on the Ubisoft platform. If Anno 117 runs flawlessly, I maybe will cancel the preorder on ubisoft and get it on Steam...
