Hi, let me answer
1- The inverted gravity was made on porpouse cause it changes how the physics work, making you need to be more in a rythm to pass through the levels. It also wasnt just an addition cause I could, because I designed all the levels around the inverted gravity and physics.
2- This is the first time someone said movement is in flaps, could you go more in depth of what you mean?
If you got more questions send them here. Also for more help in understanding the game's controls, theres 4 tutorial levels called "guides" in the level select, or you can spawn a player instance for testing jumps