Setup an unprotected network that is isolated and you fully control, see if it connects at all.
That’s what is so insane about this conspiracy theory. It would be trivial to prove yet somehow no one has ever gotten around to it.
Because you can't possibly prove it won't happen in the future...
Easiest rule in security is to just disable unnecessary services. If you are never using the WiFi, you might as well disable the hardware completely
It may be trivial to prove again and again, but it is even more trivial to just disconnect it