This was a really fun prototype! 😄
The platforming feels great, and the unique jump mechanics really make you think instead of just relying on quick reactions. Especially the harder level I actually had to use all the mechanics you'd already introduced, which is a sign of really good level design. That's something you don't see very often!
I also noticed you've already started thinking about the player experience (UX), and I think that's an important part of reaching a solid proof of fun. It's nice to see that kind of attention this early in development.
My only small suggestion would be to change the color of the player cube. Right now it blends in a bit too much with the level, so making it stand out more would improve readability.
Other than that, great work! I'm excited to see where this prototype goes. Keep cooking!