Netinstall is always limited to single ethernet port ... either management/boot port (on select device models) or ether1. And it's not selectable.
While I've also initially thought the OP asks for an USB Ethernet adaptor to be connected to the Mikrotik via USB, the requirement for ability to see neighbors in Winbox and the admittance of USB C connector suggest that he actually needs one for a PC.
I have good experience with Axago ones (that support even VLANs if used on Hyper-V). Right now I have connected a mAP lite to Axago ADE-SG, Winbox can see the mAP lite among neighbors, and I can connect to it using Winbox. I'm not going to try netinstall as it would require too much fiddling, but it's all IP traffic (including MNDP which is normally sufficient for neighbor discovery by Winbox), so I suspect the issue with the UE300C may not be Mikrotik specific.
However, gadgets available in my country may not be available in OP's country, so the value of this information may be limited.