Why not just run tailscale? U can self host head scale to keep it all first party. Tail scale i s essentially just a fancy wire guard wrapper.

I agree that straight up using Tailscale would likely be easier. But to answer your question, you’re looking to “push routes” because what you actually want to do is “route” but that’s kinda hard to Google haha. This looks maybe promising: …freebsd.org/…/wireguard-how-to-route-another-sub…