I ran into a similar problem with tailscale. It looked like I needed to disable source NAT but that didn’t appear to be implemented in the FreeBSD package so it didn’t work for me. If you’re in Linux it might be worth a shot.

--snat-subnet-routes=false

“Disables source NAT. In normal operations, a subnet device will see the traffic originating from the subnet router. This simplifies routing, but does not allow traversing multiple networks. By disabling source NAT, the end machine sees the LAN IP address of the originating machine as the source.”

https://tailscale.com/kb/1214/site-to-site

Yeah you’re right. Scratch that then

Something like mergerfs? I think this is what Unraid uses if I remember right.

https://github.com/trapexit/mergerfs