you won’t even give them that in this kind of system. you will get a user hash that is based of your signature, the system your using’s key and some mux of time and entropy input. This hash will be how they track you in a database and as systems evolve could even be a way to communicate with the user directly (like email) without knowing or holding any PII/NPI
Anything you assign to them would be data they have (maybe a common display name). Anything truly important that needs to be up there can be encrypted with different techniques that would allow the provider to work with your data without ever having to access or decrypt your data.
so the idea of them “needing to have something” to function is true, but fundamentally, they don’t need as much to operate in this system and its possible to have standards that enforce security on your more sensitive details that are sent. Imagine the security of your data, on thier system, still being ruled by your security. Even if hackers get in and copy the entire database its effectively useless.
reddit’s been less accepting of truth year over year for 16+ years