Mozilla designed a decentralized authentication protocol back in 2011 called BrowserID, which was later standardized by the IETF. IIUC, it was similar to OpenID but sites would authenticate your identity with your email service provider. Unfortunately, the protocol never gained traction.

https://en.wikipedia.org/wiki/Mozilla_Persona

Don't we already have that with WebAuthn? It should be possible for the authentication request to be directed to the password manager. Less secure than using a hardware key, but more secure than password, email, or text message authentication.

Something like OpenID connect?