Use of screen_hint signup with Universal Login and social connections only

We’re using Auth0 Universal Login and have only social logins (with Google) enabled.

In our NextJS app we’re using NextAuth to handle the authentication. I was getting an error when sending screen_hint: "signup" in the authorization parameters. After much Googling I eventually stumbled across this FAQ:

This suggests that you can’t use the signup screen if using only social connections.

I understand that strictly speaking they are not signing up for a user account but I think this is confusing to the user during registration. If it’s not possible to use the signup screen could we at least customize the text that’s displayed on a per request basis?

Further to the above, I can confirm that the screen hint does work when I create a database connection to enable username/password login.