The character class’s mesh is actually a skeletal mesh - there are bones, animations, physical assets and more. You’d need to create a skeletal mesh that Mesh(CharacterMesh0) can utilise. Do note that the character class inherits a lot of stuff already and has a ton of functionality of its own that you may not need or be unable to use since you want a simple ball instead.
Again, do consider using a pawn + floating pawn movement comp if you’re after simplicity - especially when you’re starting out.
Maybe this is the reason why IsFalling always true?
Unlikely. The movement component only cares about the capsule at the root. We’ve yet to see how you test it. Impossible to guess.