What do I need to enter to get the email of the user in a relationship? Tried

.select('*, user:users(email)')

and

.select('*, user:auth(email)')

already.

user_id uuid references auth.users(id) NOT NULL

You can't access auth schema from the api. You either need to set up a profile type table in public: https://supabase.com/docs/guides/auth/managing-user-data You could also use an rpc function, or possibly a view without creating a table in public.