Why gone?
It’s not available both UE4 and 5 and it’s normal that you cannot add f ex “C key” inside of a blueprint, nor Action/Axis mapping can be added there
What do you need it for there if UMG can contain a lot of Interactive stuff and stuff like Functions and Events can be rubbed from outside (f.ex. Player Controller)
Spawn the HUD from PlayerController, create a reference variable for it and if you need something on a key press - do it from there