Wow, love how it blends 3D and 2D. Honestly the 2D Levels look amazing, this art style's genuinely so good!!
Though I feel like the game may benefit from variable jump height for less float-y jumps on level 1, overall it's pretty cool and fun :)
Another thing is in your 3D levels, the lack of camera movement was really disorienting so it wasn't really fun. I can see the potential of a fixed camera angle and it definitely is a more "strange" approach but you'd need to atleast let the player look around and view the level. I think a mechanic of memorizing the world layout and remembering the level layout and then tackling it with a limited view could genuinely be pretty fun!
Assuming you're a starter in gamedev/godot, I'd say you're on the right track but I'd say even a short but polished single level would feel better than 6 levels which may not feel amazing.
Keep it up!