If you are trying to convert a machine from Managed to Unmanaged, simply uninstalling SEP sometimes leaves behind the "heartbeat" attempts to find the server.
Check the official Broadcom SEP documentation or visit the r/Symantec Reddit community for ethical deployment advice. If you are trying to convert a machine
: The client operates using its own local security policies, which cannot be modified remotely by a network administrator. Methods to Obtain the Unmanaged Client If you are trying to convert a machine