Am I only the one who finds it weird to have a sound slider on the menu screen without any audible feedback? :D But that aside: love the concept! The visual design is very simple, yet enough to get the idea (even without looking at the wall of text presented under "How does this game work?").
In terms of progression: I would disable movement on the y-axis (both for the camera and the player) in the first level and then introduce those one-by-one in level 2 and 3. As of right now, you can lose track of your character as early as in level 1 if you hit the wrong keys - without any explanation presented by the game. Also, as others have already pointed out, the scroll speed could be a bit higher (or somehow adjustable, e.g. by pressing shift) and collisions with walls would benefit from audio feedback.
Would love to see more challenges (like moving or deadly obstacles) added to the later levels.
My game: https://njamster.itch.io/wonkey (playable in browser)