Assume the device is no longer contactable

Grab the Entra Device ID of the device

Navigate to https://security.microsoft.com/interoperability/api-explorer

Change to a Post, paste in https://api.securitycenter.microsoft.com/api/machines/$EntraDeviceID/offboard

Add a comment in the field such as

{"Comment":"Offboard machine by anonit job number 1234"}