If you decided use the New Input System with UI you can have some problem - UI wouldn't react if you use your custom Input Assets. By default when you create the Player Input component (by default the field UI Input Module set to None) If you after that create the Event System (its create automatically if you create some UI element, by example - button), It have the default value in field Action Asset (DefaultInputActions). In this case all will work fine, but you "Player Input system" and "UI Input system" will use different Input Action Assets (in my example, the "Player Input system" use the my custom BaseControl.inputactions). More correctly use the one Input Action Assets and set the field "UI Input Module" (based on official docs - you must set your InputActionAsset in "InputSystemUIInputModule" and link it to your Player Input through the field "UI Input Module") BUT VERY IMPORTANT (its not writing in docs) you must have correct Control Scheme set for UI Actions (in your InputActionAsset). You must whether no any schemes (as on picture below) or have right scheme which will activate Action as for your Player Input System and also for UI Input System. I had problem then I set for Player Input System control scheme which used only the keyboard and its blocked any input actions to UI from mouse, because initial the mouse device was absent in my control scheme (You can set the used Control Scheme for Player Input, but for UI Input System you can't do it, it use the same).