On the app's welcome screen, Continue with Google and Continue with Apple now create an account if none exists for that Google or Apple account. No username or password is needed. If an account already uses the same email address, it is signed in and the provider is linked, as before.
Apple on iPhone passes the name Apple has on file the first time, so the new account starts with it. If Apple hides your email address or the team requires an invite code, the app says so and no account is created. Continue with LinkedIn still signs in to existing accounts only.