This looks awesome! I use a paid VPN mesh service called Tailscale to build k8s clusters which can span across cloud and home setups, but was always frustrated that the Tailscale server component is closed source. Netbird seems to do pretty much the same thing, so maybe I can switch over to it once it's stable enough.
There's an alternative to tailscale service called headscale https://github.com/juanfont/headscale (CLI only server compatible with official tailscale clients)