You’re going to love SolidPods, honestly. From the website:

Solid is a specification that lets individuals and groups store their data securely in decentralized data stores called Pods. Pods are like secure web servers for data. When data is stored in a Pod, its owners control which people and applications can access it.

I see no possible way that a centralized identity can be more private that an array of separate ones.

Check out the specifications as well, using Pods you could have seperate accounts on every platform linked only by the ability to login using your Pod.