By default, Lansweeper can only get MAC addresses from devices in the same network subnet as the server (using ARP) as well as from SNMP, SSH, WMI, the Lansweeper agent, or others. We had a large number of devices that do not support any of those protocols such as smart TV’s, our VOIP phones, and time clocks to name a few. We needed a way to identify these devices beyond just an IP address. We also wanted to be able to see which ports devices are connected to on our network switches, which Lansweeper user Mac Addresses to map. Here's a guide on how to get all the MAC addresses from your Windows DHPC server into Lansweeper using PowerShell. Note this is not at all endorsed by Lansweeper and is a bit experimental. Let me know if you have any ideas for improving this method.
https://ethanthekiwi.wordpress.com/2020/05/09/lansweeper-get-asset-mac-addresses-from-every-subnet/