This was good fun! I only had time to do one play, but I got up to level 11 or so. Enjoyed what I saw!
There could have been some changes made with some things. The game doesn't really get anymore difficult as it continues, so you could just go forever at this point. Additionally the powerup pickups can fall onto the floating platforms, making them impossible to get. It'd probably have been a good idea to allow powerups to fall through those platforms.
Other than that, good stuff!
I've never heard of Kotlin before (relatively new to programming), is it an easy language to get into? Why did you choose that one?