I’m using Synology NAS on DSM 7.2-64561. I was able to install Tailscale and share out to a friend who is using an unraid server and he was able to share in with me. He was able to mount the folders from my Synology NAS, but I’m unable to mount a remote folder in my Synology NAS. I did some testing and installed Tailscale on my Windows device and was able to access the shared folders.
So this is a pretty easy fix. Since DSM 7 apps have been locked down to what they can and cannot do. TailScale by default is unable to add a route. That means that the Synology cannot see anything on the Tailscale network. It get around this you just have to add a cronjob to allow Tailscale access to the routing table.
Follow the applicable steps in this tutorial and it will be able to route: