I’m not too sure what you mean, for their own users yeah they can use whatever their users agree to. Phone numbers, IP address, name, email, device, whatever they like really. They can then easily have that all linked up with their relevant Instagram and Facebook profiles for advertisers. Adversisers then kind of build up profiles about users across different services which is why often if for example you look up cats on one app you might see a cat food advertisement in another
Target for example is great at building profiles up (automatically) of their shoppers, a while back there was a huge story about them predicting a pregnancy Forbes Article
Other users not on Meta I’d say no, this sounds like it would be illegal honestly at least in some countries though I don’t know enough about privacy law to say
That said, instance owners could definitely sell off your data to advertisers if they wanted to and it was in the TOS of that instance
No worries at all, there’s a lot of misconception around defederating and the number of posts and comments I’ve seen really made me second guess myself to the point I had to start up some accounts across different instances to test
I think the Meta/Threads news really hasn’t helped with people spamming it like crazy