Give Espresso a try!
https://extensions.gnome.org/extension/4135/espresso/
Edit: I just tested Caffeine extension. The top bar icon does change to a hot boiling cup of coffee with smoke when it’s on, and when it’s off the top panel icon does change to just a plain cup with no heat emitting from it. You should be seeing that too, if not perhaps it’s your icon theme
Edit2:
when it’s off:
when it’s on:
