AHA! The Hitboxes are totally wrong. I clicked way off to the right and could now press the buttons. This is really weird. I'm afraid, but even for windows users (with different resolution or different GPU or...) that could cause problems. I understand, that this is hard (impossible) for you to reproduce, but that issue needs fixing.
I don't know which game engine you are using, but the big ones (Unreal, Unity, Godot) will also allow to export as Linux. If you have time and nerves (and like), look it up and try to create a linux version. Then we (at least me) can test this more thoroughly. Just give me a wink.