DaasYochid -“That doesn’t address havara.”
It’s the same with Havara -it has to be Dumyea L’mishkon & electricity is Not!
“The fact that R’ Moshe holds a microwave is D’oraiso, despite the fact that they didn’t have them in the mishkan, shows that you have fundamentally misapplied the concept of “dumya d’mishkan”.”
Who said? Maybe R’ Moshe held a microwave is, but not necessarily a different appliance. Perhaps the reason he held so was because the cooking is quite fast similar to a flame! If you want to prove something from a Teshuva -how about copying it and posting it first?