Why are you trying to save the refreshToken? Is this for the client or server? RefreshTokens are signed, encapsulated and stateless, the benefit of them is that the server doesn’t need to persist them as it’s able to read them and verify them per Request.
One limitation for Refresh Tokens support is that it must be configured to use a User Auth Repository which is the persisted data source used to rehydrate the User Session that’s embedded in the JWT Token.
But what you are saying is true about the token having what is needed to build a new bearer token.
Yeah that documentation refers to needing to either use an Auth Repository or implement IUserSessionSource in order to be able to generate new JWT Bearer Tokens without needing to re-authenticate (as typically JWT’s are created at Authentication). But as each are signed and stateless, the server never needs to persist JWT Bearer or Refresh Tokens.