Wow, this was something different. Beautiful looking game, great atmosphere. You made all this yourself or did you use some assets?
My biggest concern with this game is the camera movement. When you're at the bottom of the map, the player character doesn't have to be in the middle of the screen. That just makes half the screen filled with useless black ground. This can be solved by setting a float minHeight variable that is set each scene. Also, when you jump far the camera is sometimes too slow to follow you. Hitting spikes when you can't even see your character is an extremely frustrating way to die. I'm not sure how you do the camera movement, but I'd increase the movement speed of the camera if it's far away from the player. These should both be fairly easy to implement. Basically, my problem is that I can't see all the obstacles. Maybe simply zooming out a bit would help as well? If you can afford game assets, this is a really good 2D camera asset that I've been using: https://assetstore.unity.com/packages/tools/camera/pro-camera-2d-the-definitive-...
Now, I really like the atmosphere and the art style of the game. But why is the main screen so much different from the game itself? :P At the start menu it feels like I'll get some action-packed sci-fi game, and the game itself is a really pretty, fairly calming (except when you die from spikes for the thousandth time...) game with a great atmosphere.
Finally, please add a way to exit the game without having to press alt + f4. The super simple way is to add a PauseMenu object that is inactive in your canvas, and when the player presses escape this gets set to active. In the pause menu, all you need is a button to continue the game and a button to quit. Application.Quit() will close the game. This takes 5 minutes in total.
Good luck next game jam! :)