How widespread OpenID actually is? I remember creating an account a decade ago, but I've never used it much (in StackExchange only I think). Because any fearure we add is something that needs to be maintained forever afterwards, so if it's only for one or two users it doesn't make much sense.

It would also need to be optional since supporting this for example in Joplin Cloud would not be easy (since account creation is via Stripe).

Finally remember that it needs to work in mobile too. Many npm packages assume a Node environment which is not present in React Native.