As an alternative you can inject the builtin property in opencore: First of all check that your ethrnet card is recognized as en0 in macOS; if this is not the case delete the network properties (you can find easily how to do it in google), attach only the ethernet card and reboot, so that macOS will pick up the card as en0.   Download the release version of gfxutil. It's here: https://github.com/acidanthera/gfxutil/releases/download/1.80b/gfxutil-1.80b-RELEASE.zip  
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