When creating a new Workspace in GCP the default GCP External Location is wrong.
Its easily fixed by Catalog (on the left) > External Data (on the bottom) > External Locations > choose the connection and edit the URL by deleting the second BucketId after the /
(gs://databricks-xxxxxxxxxxxx-unitycatalog/xxxxxxxxxxxx => gs://databricks-xxxxxxxxxxxx-unitycatalog/ )
Test the connection. Ready to use.