BeaglePlay's USB network forwarding on the host?

I normally don’t have problems with setting up my host machine as router, this works for my other devices connected over Ethernet cables to my docking station, so I can NAT traffic over my WiFi link. But usual tricks with setting up NAT still don’t let the BeaglePlay connect anywhere else than the host it’s connected to.

What am I missing?

Is there limitation of the USB network interface on Ubuntu 23.10 that I’m not aware of preventing this from working? What I see the IP addresses are fixed, but no default route is set on the BP, but setting that manually doesn’t solve the problem.

Is there any guide how to do this right?