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so created the profile table from the template. would u create a user profile after user confirms account or after user registers

This is up to you the developer, I tend to create it as soon as they register using a trigger and a function

https://supabase.io/docs/guides/auth/managing-user-data#advanced-techniques

is there a way to pass in a random generated username to profile

Combine it with https://dba.stackexchange.com/a/246467 and you can get a unique generated random username