A logic question: When using Hasura in combination with Supertokens, is it common to

insert

the user afterwards into Hasura through the

emailPasswordSignUpPOST

signup callback?

Depends on what you want to do. You don't need to insert the user ID into Hasura if you are not storing some extra info which supertokens can't store for you.

Well I need the user in my DB for relationships etc. So I have to insert the user into my own database as well, after signing up. Or how would you recommend to do this differently?

if you need to relations, then go ahead and insert them 🙂

exactly, thanks