Editor is missing a font and is quite broken in web export. I left it as it kinda works sometimes and was really helpful for me, also spend a lot of time on it. It should work correctly if you get the source and run it in godot. But its not intuitive :)
Quick editor tips: - you select "nothing button" and press space to play music - when playing music use qwe to place notes - editor auto aligns notes, if you want more often beats use +/- keys to change *2 - remember to set correct BPM (in godot track resource) if you change the audio track - you can use mouse to remove incorrect notes - you can use mouse drag to rewind a bit - save updates track resource, its a text file that nicely shows changes if you use git - when you get those weird notes at the start something broke, reset might help