If you are not able to connect your PC to your mobile device, using Syncthing in both of them, you should check your firewall, both on PC and on mobile.
And, of course you have to set, in firewalls, permissions to communicate each other.
KDE Connect not working
You have both smartphone and PC connected at the same network. But no connction between the two.
1st case
A possible reason is a firewall on the smartphone, .i.g. ReThink. In this case you should exclude KDE connect from firewall.
2nd case
If you have a KDE connect connection, but you cannot browse your decive from your PC, you could have some previous corrupt installation/config on your PC.
Than you can try with:
- killall -9 kdeconnectd kdeconnect-app kdeconnect-indicator
- then no output for: "pgrep -la kdeconnect"
- rm -rf ~/.config/kdeconnect ~/.cache/kdeconnect ~/.local/share/kdeconnect
and then
- systemctl --user daemon-reload