Hi Fadi Helou,
Thank you for reaching out to us on the Microsoft Q&A forum.
For protecting devices through Device Serial Number ACL, you can use Access Control Lists (ACLs) to filter traffic based on device serial numbers. Define rules that allow or deny access based on device serial numbers and MAC addresses. Apply these rules to network interfaces to control traffic.
Please refer the following link for Microsoft Defender for Endpoint on a local network without a domain server: https://zcusa.951200.xyz/en-us/defender-endpoint/configure-endpoints-script
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