I remember seeing a tutorial for making a platformer in game maker ver. 7 (which was from 2 decades ago) explaining how to make the camera lag this way. I've also played a few 90's dos games that made the same mistake. I think this might be the first time I've seen it done since then. Let me be very clear: letting the camera lag behind the player is bad, and if you got that from a tutorial stop trusting that author. Unless it's a moment where the only important thing is emphasizing the character's speed (like a cutscene in a sonic game), that will always be more of a nuisance than anything else. If you don't have a good reason to do otherwise, just keeping the camera centered on the player is typically the best choice. And even then the 2 first things to consider as alternatives should be not having the camera always go up when the player jumps and having the camera centered a little in the direction the player is facing (like Donkey Kong Country and Super Mario World do) so the player can see more of what they're running toward.
Other than that, I would advise making paths in levels more clear unless you can make the game runs far quicker than this. Trial and error gameplay needs to be really quick to not game frustrating. It's also a good idea to make sure any required leaps of faith or drops are completely safe and consistent (referring to the drop after the key in the first section, which can land on a skeleton). Otherwise you erode the player's trust that you're not just messing with them.
Also, I highly recommend against repeating elements in sequence, and especially when it emphasizes awkward and janky parts of the mechanics. When I got to the part in the vertical section where the platform start being on the left, I just stopped.
Lastly, in case you decide to make a platformer again, be it for a jam or otherwise, here's some advice: the very first thing you should do is make a test level with platforms of about the size you want for the game then create and tweak character movement. This includes setting gravity, initial jump speed and the increase in gravity when the player releases the jump button, and also making sure all of that feels good with the horizontal movement. All of that should also take into account the size of the character on screen and the actual character sprite if it's available soon enough (because the nature of the character and the size of their legs can affect the feel). It's also a good idea to ask someone else if it looks and feels good to them really early on. The reason this is so important is that moving is always the thing the player will be doing most in any platformer (and most other action games), so nothing else will feel good if the movement doesn't.