Hi @Glenn Maxwell ,
Per my test, it’s currently not supported to disconnect the SharePoint Site from the O365 Group. This behavior is by design.
As an alternative, I would suggest modifying the settings of ug1 to ug2.
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
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.