Is it possible to link additional (social) providers to an existing user/account? Can't seem to find anything in the docs about this.

Yes, if they share an email they are linked... https://github.com/supabase/supabase/discussions/3098

Thanks, will give it a look! I see that it’s common case to rely on the same email but that might not be the case nowadays. Especially like for myself, I sign up with Hide My Mail on all the places so it’s different everywhere.

I did not want to mess with any localhost issues when testing redirects so just install in on a "test server" on the net when doing that kind of stuff.