After a ton of attempts with setting up multiple device VPN with #wireguard, I had to settle on one-interface/config-per-device. I just could not make this work any other way. Fortunately now I can actually do some routing on top of my point-to-point mesh.
The downside of this approach that you a) create a lot of interfaces on the server (one per connected device) and b) waste half of the IPs on server point-to-point addresses. That said, even a measly /24 is more than enough for me.