I've tried Proton 9.0-4, 8.0-5, GE-Proton10-4, Experimental, and Hotfix.

Without fail, game shows the title card, then opens another window that captures my mouse (have to Alt+tab) but is just a black screen.

Left this running all night (6+ hours) and managed to get to the warning screen and Ubisoft animation. I never made it to the title screen.