I have two Instagram accounts and I created a Threads account on one. Searched for the other and there’s nothing I can find for it. Definitely can’t follow the second account on Threads.
I’m not trying to be a Meta apologist here. I trust them about as far as I can throw a car (especially given the insane amount of data collection mentioned in the App/Play Stores) but in my limited test I don’t see a way to follow an account until you activate it on Threads