This is a great game! I really liked the visual style you went with and the music and sound design fits really well. I love the clicks when you shift gravity. Level 4 was my favorite, it was a really fun use of the gravity switching. I also feel like level 4 and 5 were a natural progression where level 4 taught you to manipulate the cube in 2d to introduce the mechanic, and then level 5 tested you on it in 3d.
I think puzzle games are the hardest genre to do in a jam because they rely so much on playtesting with people that don't know the solutions. My only real criticism can be ironed out easily through some playtesting. Level 1 is pretty difficult because you're placed in the big room with the controls on screen. I accidentally hit H to hide them, but I didn't get to read far enough to know that was the hide controls key to bring them back. It took me a long time to figure out what to do with the cube, and then that cube was never used again. Level 2 felt like a great tutorial for gravity switching since that was the only mechanic in the level, and level 3 starts with an excellent tutorial for the book. Not letting you leave until you get it right, plus a hidden coin that's easy to find with gravity manipulation. I feel like the game might have been a bit better if level 2 was the first level, level 3 was the second, and level 1 was the third level while replacing the block with a book.
Picking up items is also a bit difficult because the press E to pick up appears at a distance further than your grab range. I think highlighting the object at the current range, and then not displaying Press E until your in grab range would improve the feeling a lot. I was confused why pressing E wasn't doing anything until I moved closer.
Excellent job!