Can’t remove additional onmicrosoft.com domains created during SPO domain rename preparation

[Microsoft User]

SPO domain rename involves adding at least one new onmicrosoft.com domain to the org’s AAD tenant.  When I did this a few months ago, I was able to 1) create more than one new domains, and also 2) delete any newly created domains I didn’t like.  But now it looks like it’s no longer possible to delete any unused onmicrosoft.com domain.

Tl;dr —

1. Org’s initial domain is contoso.onmicrosoft.com.
2. Org adds fabrikam.onmicrosoft.com and adatum.onmicrosoft.com to the tenant.
3. Org performs SPO domain rename with the adatum name.
4. After a few months, deleting fabrikam.onmicrosoft.com (which is not being used by any resource) is no longer possible.

I’ve tried doing this with the Azure Portal, the AzureAD and MSOnline PowerShell modules, as well as the Microsoft Graph API directly; all came back with the “operation not allowed” error.

Is this the expected behavior or a newly introduced bug? Can I contact Support to have the unwanted domain removed?

[#2]

Good morning, best way to perform and contact microsoft to avoid future problems. About the powershell error as you are trying to remove something from the organization fix the organization permission for your user.
Go to office.com>administration>exchangeonline classic mode
When entering classic mode, in the left corner you have the permission option.