Oh, hmm i thought itch let videos be embedded but looks like it is just images dang!
Okay so the reason it's only drawing on the one frame is because by default loop draw is looping over all the frames in the timeline. Because you've only got the one it's painting all your pixels there.
You can either add in some more blank frames, I belive the hotkey in Aseprite is Ctrl B, and then it should loop though the cels / frames when is looping is on. This is where you toggle is drawing and just move (not clicking) on the canvas 😀
The other option is in the adv settings called Append Last Frame. This will keep adding frames to the end of the timeline (after the last frame) instead of looping around.
Again sorry for any confusion on this. I hope I can some how find a work around in the future for using the mouse click instead of the toggle but yeah its tricky stuff!
Let me know if this helps though!! 😀