I was unclear, sorry! By buttons I meant the UI Element not the input mapping. When I use UI Buttons in a scene with UCC controller characters the buttons can't be pressed and mousing over them doesn't change their color the way it should.The demo scene uses the old Unity input system. The button mappings are defined in the Project Settings -> Input Manager -> Axes. The UnityInput (inherited from PlayerInput) component then does the mapping from the input system to the UCC components. There are also integrations for the new input system, and for external solutions like Rewired or Control Freak.
But you can always check input independent from UCC