Exposing LAN with Zerotier when using Ubiquiti Edge Router X?

You have a choice between layer 2 bridging and layer 3 routing. We don't have much direct experience with Ubiquiti but you can find a lot of info around about doing either of those things. The ZeroTier interface should show up as another interface on the Ubiquiti that you should then be able to route or bridge to/from.