Unfortunately, I think you have a fundamental assumption that JWT is and authentication mechanism, which is wrong.

JWT is just the token format that's being by authentication mechanisms, such as OAuth/OIDC, or even new emerging standards like Decentralized Identifiers (DIDs) and SIOP.

Those authentication mechanisms provide definitions of flows that cover not just the basic "user identifies to backend" scenario, but more complex scenarios such as establishing trust between two security boundaries.

If you are really interested on decentralized authentication and authorization, I do encourage you to take a look at Decentralized Identifiers, which can actually be used not just for authentication scenarios (you can start here: https://www.w3.org/TR/did-core/).