Hub Workspace with Centralised Lakehouse

Hello VictorMed,
Looks like the issue is the difference between workspace access and SQL security.
Your schema permissions only affect the SQL endpoint, but once users get Viewer access to the workspace, they can access the Lakehouse more broadly through the Fabric portal.
Also worth checking the removal of the DefaultReader role, since that can break normal Lakehouse access.
From what I have seen, Fabric still does not fully support strict schema isolation inside a single shared Lakehouse in the same way SQL Server does.
Most people end up separating access using different Lakehouses, workspaces, or semantic models instead.

Docs:
Data security overview 
SQL granular permissions in Microsoft Fabric