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This adapter is for a Thunderbolt 1 or 2 Mac, not for a Thunderbolt 3 one like your 2018 MBP. So, you'd need a Thunderbolt 1/2 <-> Thunderbolt 3 adapter on top of it.

It's easier and much cheaper to just get a USB-C to gigabit ethernet adapter.
 
Well, the official Apple dual adapter combination is a.) natively supported wthout drivers, b.) supports netboot and internet recovery and c.) supports network offload capability to lessen CPU load and achieve actual gigabit throughput.
 
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