@fjc1029 MeWe is and always has been just a plain centralized service.
A self sovereign identity provides cryptographic verification that it's actually a certain entity who's posting on that (or any) platform.
Like using Github with GPG for signed commits.
How data for such an identity must be structured and how to verify it actually maps to a physical (or legal) person is the problem many tried (with so far little success) to solve:
web of trust (GPG)
multiple fully trusted authorities (x509 certificates in browsers)
pubkeys on a blockchain (Bitcoin, source of a transaction) or
deterministically derived from verifiable data (Bitcoin, target of a transaction)
or any combination of those (Google certificate transparency, GPG web key directory, etc.), when the pure approach did not live up to its promise.