This can happen if a macOS restriction profile applied from Hexnode is blocking account changes.
Check the macOS policy associated with the device and review the Advanced Restrictions section. Look for the restriction named Modify Account Settings. If Modify Account Settings is disabled, users will be prevented from adding, removing, or modifying accounts in System Settings. This includes signing out of an Apple ID. To allow Apple ID sign-out and account changes again, enable Modify Account Settings in the macOS restrictions policy and make sure the updated policy is associated with the device.