My understanding is that it’s automatic when the President is “unavailable” to perform his duties. Whether or not PDJT was really unavailable is irrelevant to these people. They create the fake emergency and make whatever designations they need to to make it look correct and necessary. We all know here that that’s insufficient cause to designate Pence CIC, but laws and truth do not matter to them, only their end goal. On J6, Pelosi’s goal was to stage a coup.
I point you to the Constitution and the 25th Amendment.
VPOTUS does not have C-in-C until such time s/he is sworn in as POTUS.
Again, Al Haig was NOT wrong when Reagan lost consciousness.
The Joint Chiefs are C-in-C until POTUS recovers or VPOTUS is sworn in.
That is an “originalist” interpretation of the Constitution and 25th.