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I understand that you are trying to delete the groups in GCP, but you are facing an issue stating Google does not support reversible (or "soft") deletes for this type of object.
Based on the error message it states Google Workspace does not support automatic deletion of groups through the provisioning connector.
Try to remove the groups manually in Entra ID which is instructed Remove users, groups, or devices from an administrative unit you can perform single or bulk operation.
In the same way you can Removes an Active Directory group and see the synced groups has existed in the GCP.
Also, as the error message is from GCP I would suggest reaching out to Google Cloud Customer support
Hope this helps. Do let us know if you any further queries by responding in the comments section.
Thanks.
Akhilesh.
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