For those who may find this thread via Google in the future, I finally got a longer ethernet cable and was able to determine that no, even hooking up to the LAN port and running a cable from there to the MoCA adapters, and then to the second AP, I still could not get ethernet backhaul working...
I have two XT8s and a mandatory router provided by my ISP (Verizon 5G). I connected the two XT8s in AP mode, with wireless backhaul.
I've been frustrated with the wireless backhaul performance and wanted a real hardwire backhaul. Since my house is not wired for ethernet, I opted for MoCA 2.5G...