Oh, it seems that AppImage requires FUSE 2, but you only have FUSE 3. Interesting! What distro are you on, out of curiosity? On Arch Linux there are 2 packages: fuse2 and fuse3, I have both of them installed.
Yeah, it’s tricky to find a window for the cooldown! :-D But you don’t need to cool down all the way to 0%, I usually try to keep between 60% and 90%, because the laser actually deals more damage when it’s heated more.