Comment # 1 on bug 1083884 from Frank Kruger

(In reply to Graeme Blackman from comment #0)
> OS: Leap 15 dupped to Build 147.1
> 
> With the move to firewalld, the syncthing install on Leap 15 (TW also ?) no
> longer sets up the required firewall ports. i.e. 22000 (tcp) and 21027 (udp).
> 
> The firewalld service file required for syncthing,
> /usr/lib/filewalld/services/syncthing.xml, would contain:
> 
> <?xml version="1.0" encoding="utf-8"?>
> <service>
>   <port port="22000" protocol="tcp"/>
>   <port port="21027" protocol="udp"/>
> </service>

Syncthing was introduced with firewalld 0.5.0, which provides syncthing.xml:
<service>
  <short>Syncthing</short>
  <description>Syncthing is a Peer-to-Peer file synchronization service. Enable
this option, if you plan to run the Synthing service.</description>
  <port protocol="tcp" port="22000"/>
  <port protocol="udp" port="21027"/>
</service>

See the request at https://bugzilla.opensuse.org/show_bug.cgi?id=1084026