Hello @DSDV, please clarify if you tested the main game or the demo. In general, the demo of a game has a separate AppID and might have separate technical requirements, so they're treated as separate games in terms of troubleshooting.
Additionally, please add PROTON_LOG=1 %command% to the game's launch options, reproduce the regression, and attach the generated $HOME/steam-$APPID.log to this issue report as a file. (Proton logs compress well if needed.) Also, please copy your system information from Steam (Steam -> Help -> System Information) and put it in a gist, then include a link to the gist in this issue report.
PROTON_LOG=1x1 2025-06
Compatibility Report
System Information
I confirm:
Symptoms
mouse escapes the game and moves to other monitors
Reproduction
on latest proton 10 when pressing or holding some keys like the thumb mouse buttons 4 and 5 the mouse escapes the game and moves to other monitors.
Workaround
this can be worked around by selecting an older proton version like proton 9