

The routers or computers you are using for this have to support forwarding traffic. With Linux this is pretty straight forward for other OSes I’m not sure how easy it is.
You can get around this by having tailscale installed on the default gateway (router) of each network. It might be quite a pain for OP to change routers at each location. On the plus side, OpenWRT has some other cool features like PXE booting.
You can setup wild card certs with a DNS challenge using traefik. No plug-ins needed, works right out the box.
Personally, I quite prefer traefik. Its harder to use than Caddy but offers more features. Also, it uses yaml or docker labels for config. I’m not a fan of the nginx .conf format.