You did a good job with your first game jam. I feel like there is a lot of potential here. Unfortunately with the crashing bug, it does make it difficult to play. Something you might want to think about adding for the future would be a level select screen or a skip level option. Even without the game crashing, having the those things can give players more options, particularly if someone wanted to come back and play more later but doesn’t want to replay early levels.
I liked your use of the color swap when switching gravity. It could feel a little flashy if done too quickly one after the other, but it felt like a good way to quickly and easily convey information to the player. I thought it was particularly useful at the start of level 4, when you started on the ceiling instead of the floor. On that note, I really liked that level 4 started on the ceiling, since you ended level 3 that way. It helps give the game a connected feeling, instead of a bunch of individual levels.
I sometimes found myself wanting to push the down arrow when I was on the ceiling to jump, so a couple of times flipped the gravity when I meant to jump. If you decide to change the flip gravity button to something else, like space or shift, you may want to have jump switch between the up and down arrows based on the gravity. That said, I also think it’s just fine to leave the controls as they are, with up always being jump and down being gravity flip.