[MandK]

Assume we’re talking the water heater? Our 2021 has the on/off switch on the water heater and two switches on the panel inside, one for electric and one for gas. Clearly marked. The one on the water heater itself stays on all the time unless I’m going to drain the tank for winterizing. Turn it off then so that if you accidentally hit the switch inside, it won’t fry your heating element from not having water in the tank.
I have seen posts here before from folks that had control panels with unmarked switches, in which case you might have to experiment. Make sure there’s water in the tank if you do.