This is a cool concept with an impressive scope for a game jam! Moment-to-moment gameplay feels tight and I like the retro 3D aesthetic. It's a small thing but one of my favourite parts was the music changing per biome and the matching the mood/theme of the area, that feels great as a player. I also really liked variety of levels and the overall mood and feel of the game, it felt immersive and it was usually clear where to go/what to do, alot of mechanical polish under the hood as well with a few quality of life features that I really appreciated.
Feedback wise, I would try and refine the idea (i.e. mechanics and genre fit) a little bit, first-person plat forming is a very difficult thing to pull off and make fun when combined with another idea, and I found myself wishing there was more of the spell casting and looking/interacting with cool shit and less of the fall-dying and jump puzzles. Also, it's super minor, and I'm sure you just ran out of time, but I would add some animation or visual effects to the hand, in a first person game you're looking at that weapon the whole time, it needs to have some visual interest.
Overall, this was an impressive effort, I'd be excited to see where this game went if you decided to keep developing it!