The Input and axis mappings you are talking about sounds to be part of the Project Settings input method (last supported in UE 5.1.1, and fully removed in UE 5.2)
this system was replaced with EnhancedInputSubsystem
everything that was in the Project Settings method is still viable, and even expanded upon. Instead of just getting whether the button was pressed or released, we now get held states, and combo buttons are “technically” easier, and more re-usable.
the official documentation, and a brief tutorial can be found here:
beyond that is there anything specific that you are not clear on a translation for?