You seem to be using the terms "pair" and "connect" interchangeably, but they aren't the same thing. When you tap "forget" in iOS settings, that's unpairing. Tapping disconnect is not unpairing. I have not used the WF-1000XM3 but the documentation for switching between paired devices is the same as for the WH-1000XM3.
Yes, I'm being imprecise in my language.
My understanding is that both versions of the Sony's - over ear and true wireless - can be
paired with more than one device at a time, can be
connected to only one device at a time - and in order to switch which device they are
connected to, you must first
disconnect them from the previous device.
I find this to be a royal PITA with my over-ear Sony's, and if this behavior is the same with the true wireless model, it's ridiculous this review site gives them a significantly higher score than the Airpods despite the Sony's not having a single real advantage in that category.