the UI scale is not the problem. the entire game’s scale is the problem. more specifically: you’ve set an unnecessarily large size for the embed window under the misguided impression that everyone will have their browser set to a size significantly larger than 1920x1080 (in order to contain the frame and its controls)
the game should be embedded in a significantly smaller frame, ideally the default width of 640px. when i eventually did manage to reach the fullscreen button, it was running just fine at 4480x2520, so it’s not like it only works at 1080p