based on how I swapped my tank to tankless in my 2020 Highland Ridge (it had electric and propane).
You will need a 15 or 20 amp ground fault breaker for that circuit (need the proper model type to match your 120v breaker panel), check the instructions to find out which you need, the original tank hot water system in my Highland used a 15 amp, the tankless required a 20 amp.
it MUST be a ground fault breaker, not a standard breaker, it has to have GFCI (Ground fault circuit interrupter) in the breaker.
also you need the proper 120v 12 gauge wiring from the breaker to the unit. DO NOT SKIMP on the wiring, use the proper rated wiring for the circuit, too small will get HOT and cause an electrical fire.
just going off the instructions from mine and 35 plus years working with electrical stuff.