How to view durability again?

It still works for me consistently. Try pressing F3 + Q to see the command list, and if it is changed, it should show up there. Otherwise, just make sure your F3 and H keys work independently, and if nothing's wrong there and the list still says to use F3 + H, then make sure your system isn't treating F3 + H as a shortcut to something else (not sure why it would unless you made it do that...).

Otherwise, try loading another version and seeing if it works there; if not, either your keyboard is broken, your computer is overriding or not receiving the shortcut, or something else system-related (try checking your cords), and if so, try reinstalling 1.14.