I use Spacedesk to extend my Windows desktop to an extra MacBook, and it works like viewing a remote desktop over the LAN. It's a bit laggy with WiFi, and since both machines had USB-C, I thought I ...
Unless there's no other option, you should ditch USB-Ethernet adapters ...
Some (many?) HDMI cables can also carry Ethernet over HDMI. The main use seems to be to provide internet connection to a smart TV from a cable modem box. Currently I have an ethernet-USB adaptor ...