I have items in the portal items content directory on the server, that don´t show anywhere in the portal.
The corresponding ArcGIS Server Services do exist.
Portal Item Example:

I tried this, but it did not help: Problem: Unable to View Items in the Portal for ArcGIS Content Page (esri.com)
Is there a way to assign all those unassigned item folders to a specific user as portal items?
From what I understand, this information needs to be added in the gwdb...