No local administrator group privileges on Microsoft Entra joined device

Question

A device used to be owned by a user ******@domain.com. It is MS EntraID joined.
The user was removed from MS 365 more than 60 days ago. The device had no (other) local admins so there are many restrictions.

I re added the user ******@domain.com but it did not regain the admin rights.

Then I saw in EntraID that the Device Owner was missing. I used this howto to add it:

https://www.linkedin.com/pulse/device-owner-missing-entra-id-azure-ad-valentin-komarovskiy-mba-dbjae/

I added the user ******@domain.com, but it still had no local admin rights.

Then I used this howto to correct this:

https://learn.microsoft.com/en-us/troubleshoot/azure/entra/entra-id/dir-dmns-obj/no-local-admin-privileges-azure-ad-joined-device#part-2-check-for-local-administrator-permissions

After doing this, the user STILL had no local admin rights.

I added ANOTHER RegisteredOwner, a different account, and used the same troubleshooter, but the result is the same.

Any suggestions?