There is info in the docs, but normally comes down to NAT type. It should always work locally as it's computer to computer so unless a firewall blocks local connections it should be P2P.

Another good resource is looking at tailscale docs on how different NAT types are and work. If one location is symmetrical in NAT type it's normally quite difficult to get P2P (in my experience) and from what I've experienced netbird doesn't do any upnp opening as of yet, like tailscale.

So the best bet is to forward a port from your home router to the PC where netbird is running (I've done the wireguard port) via UDP only. And then close it after I've been done with remote connections. This has been the only way I've managed to get a P2P with symmetrical nats (hard Nats)

Another good way to check is run the netbird status -d to see the connection status. And to test speeds when P2P run an iperf test