This was a really neat little game. The idea is very interesting, and could easily be expanded in lots of different ways. One way that I think would be lots of fun is adding one extra button that has different functions in different levels. Perhaps you have a Hollow Knight style midair dash in one level, and then in another the ability to turn metal and block or break certain things. Adding a bunch of different keys for abilities would give you too many platforms to work with, but one extra button that changes function would work well.
Also, right click to retrieve all placed keys would be a nice feature.