Hi @Paulschnack ,
Welcome to our forum.
When Remove-FederationTrust fails because it is in use by some listed organizations. And the federation trust cannot be removed by any method, it is recommended that you manually remove the Federation trust from ADSI Edit.
Please note: Deleting ADSI is risky, in order to prevent any errors, please back up ADSI before using ADSI.
The object to remove is CN=Microsoft Federation Gateway,CN=Federation Trusts,CN=OrgName,CN=Microsoft Exchange,CN=Services,CN=Configuration,DC=domain,DC=domain.
Please refer to the similar thread: problem-removing-a-exchange-federation-trust
If an Answer is helpful, please click "Accept Answer" and upvote it.
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.