Congrats on your game, it's a simple idea that you exploited very well.
I liked the fact that the first levels are mini-puzzles based on the core mechanic and that you only start to introduce "level mechanics" later on. Also, the game is easy to read but the neon-portal art direction keeps it interesting.
If you wanted to push it further, after the jam, I'd primarily polish the controls:
I couldn't play without changing my keyboard layout (I have an AZERTY keyboard). Unity handles it now so it's a pretty simple change.
The jump could feel better. I died doing simple jumps because of how heavy the cube is and because there's a lack of feedback on the jump. The cube could squeeze a bit before jumping, ...
The physics starts to break a bit when you hit the level with the "force arrow" pushing you up. I didn't understand at first what was happening.
Anyway, it's a great submission, congrats!