I like where you were trying to go with this but the actual implementation needs more work.
First of all, while I fully endorse a "show, don't tell" approach to teaching game mechanics, this usually only works well if the player is put into a situation where they're given everything they need and can't proceed until they've learned the new mechanic.
The text at the beginning was easy to miss, especially when you lead the player towards the right, not towards it.
The yellow area was easy to avoid, therefore I died a few times and started back at the beginning before I randomly found out it was a checkpoint. I'd either make the first one the player encounters unavoidable or explain to them what it does.
The slingshot mechanic is fun but also insufficiently explained. Some text near the orb with one sentence of explanation or even just the word "[Shift]" would've been enough.
The introduction to the slingshot orbs was frustrating. I'd recommend giving the player a safe space to learn a new mechanic where they can fail several times without getting punished. Then you could ramp up the difficulty and risk so they're forced to get better and better at it. Instead, I died to the first slingshot orb several times and immediately afterwards to the several orbs above a death zone, which feels like too harsh of a difficulty spike.
With each death I got more and more exasperated as I had to wait for the "FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF" to finish. This is essentially a long "You Died" but I think your game is not the right place for that. With the difficult mechanics and the frequent deaths, the e.g. Super Meat Boy or Celeste approach of immediately trying again would work much better.
The text that preceded the red block falling onto me was funny.
Everything seems to smear at high speeds. This is especially apparent when the camera shakes from taking a great fall and my entire screen becomes blurry/smeared.
I quit the game out of frustration but there's definitely some potential there.