Ah interesting! I'm not an expert with networking, I usually just stick to the basics of one interface and then bridge it if I need multiple things using it.
What things do work? Using ping with an interface name does some special stuff which isn’t available to programs not running as root. Did you get anything other than ping running on it - if so how?
By that I was referring to ping and curl, but I have also had VMs bind to the interface directly whenever I need to spin something up and test it, but I've always kept it within the same subnet, just a different IP.
I guess I'll have to figure out how to adapt that to systemd-networkd, thanks for the help everyone!