I mean this whole process is explicitly for the purpose of attaching your identity to your online activities. If you don't want to do it, just don't.
I shudder to think of what will happen when hackers inevitably get into Twitter servers and steal all those IDs though...
Meta applies a myriad of advanced and complicated tracking methods. Email is a very popular and easy one. I believe the one you're referring to is called a tracking pixel.
For example, some browsers block tracking Pixels, but if you're logged into Amazon with an email address that Meta knows, they will sell your shopping habits to Meta to show you ads.