Oh wow, thanks for taking the time to test it out and take a video. If you have time, could you try it again, and hit the Esc key to bring up the Main menu, then hit Resume Game and see if it grabs the mouse again? I think this might be an itch.io-specific web bug and something I can maybe code around. Or at least create a key to allow you to regrab the mouse cursor focus.
I appreciate the info on the Linux build. That is a huge bummer, as I could not test that build. However my games in the past have worked on Linux as I usually have a friend test them. Your feedback gives me something to look into though. Thank you for taking the time to do that.