How to implement SSO with BaaS solutions?

I run a Startup and want to offer one simple login for all the different web apps (which have their own branding and domains).

Because I want to save time implementing the Auth process, I looked at solutions like Supabase or PocketBase.

All these BaaS solutions have one user table for each application. So every single application would have their own User table, login process and their own conformation emails, etc.

I would like to have one User table for all applications, but app specific confirmation emails and branding.

So far I could only think about running my own OAuth server which could be realized with ZITADEL, Keycloak or Ory but that seems a bit overkill. (I don't want to use paid services like Auth0)

Alternately, I could simply create my own User Database and write my own APIs, but that would mean more workload for me.

Is there a simple BaaS style solution which can also handle one User table for multiple Apps?

Any suggestions? I can't be the only one here on HN who wants this logic?