Sorry for my bad explanation. It is “Discover” problem not “Sync” problem.
Since I cannot use port “22000” in office. I can use port “12345” only. And port “12345” forwarded to Nginx Server 443 port.
I can access the GUI outside the network, followed by this guide https://docs.syncthing.net/users/reverseproxy.html
But the Syncthing server cannot discovery by other outside the network.
And I found the post, https://forum.syncthing.net/t/resolved-expected-1-certificate-got-2-error/16015/5
He seems can config the Nginx to act as port forwarding.
But I can’t make it work.
After the above setting, When I use “tcp://syncthing.test.com:12345”, for the server address. I will got another device id (an unknown id), which is not the Server real device id.