Note that this feedback is based on the build(s) available at the end of the jam.
Conceptually, I dig this game. The idea of giving sad friends high fives to cheer them up and find out what they do when happy is lovely. Unfortunately, the high fiving visually reads as slapping, which puts an entirely different spin on things!
The art has a lovely scribbly quality to it that evokes a sense child-like play, which supports the intended atmosphere well. The faces on all friends feel like they're positioned too far to the left, leaving some facial features (particularly on frogs) floating out in the air.
I like the way that the catapults provide access to different areas of the level, but it's very easy to wind up stuck inside something (particularly for catapults where the far end isn't visible and knowing the safe position to stand requires having previously visited that area).
Ultimately though, the thing I've enjoyed most about playing this game is that things aren't immediately obvious and it's up to me to experiment and interpret what things are and how they work. Games that allow for "wonder" are few and far between these days, and in spite of its issues, Cheer was refreshing to explore.
I think you've got a good start and the right ingredients for a fun and happy experience.
Thanks for your submission and best of luck if you continue with development! :D