https://bugs.winehq.org/show_bug.cgi?id=46309
--- Comment #5 from faalagorn@gmail.com --- Thank you a lot for the help! Sorry for not replaying earlier – I wanted to provide log but didn't had the time before, but your updated patch seems to solve the issue for me :)!
I didn't test the "GrabFullscreen" to "Y" under [Software\Wine\X11 Driver] tip you provided before (I doesn't seem to have nothing set in that registry key, the only option Lutris sets is Mouse Warp Override on Default), but I guess it's not needed as of the most recent patch.
I also have a feeling that this patch might have helped prevent the issue with mouse drifting the same way when my game lost a focus sometimes (by "alt-tabing" out of it), though it's hard for me to tell when exactly did it happen, so I'm not 100% sure about that. Either way, it's definitely no worse than it was before the patch, which makes me very happy :).
I'll keep running this patch for now, but will this patch be updated in wine-staging soon as well? Or should I inform them about it too? It seems that staging patch caused some trouble for some with Valve's Proton fullscreen hack enabled, so it got disabled in wine-tkg builds in this commit: https://github.com/Tk-Glitch/PKGBUILDS/commit/1d98d5f33584f7fc2e5d60ed1c276b... so hopefully the newest version won't cause any issues there anymore as well. I didn't use that hack though, but I still was affected by this mouse drift/sync issue before the patch.