I wrote some time ago about kdeconnect and linconnect.
Kdeconnect was not working for me, empty screen, no error message.
Today I got an update of kdeconnect installed on my PC so I googled once more "kdeconnect empty screen" and found one post (sorry forgot to bookmark it) : the statement was that kdeconnect was expecting TCP ports 1714 up to 1764 to be open to outside world for device discovery to work.
Gave it a try... and could instantly pair my android device with my PC !
Now that I know this, a Google search for "kdeconnect ports" results in the KDEConnect home page being the first hit. It tells :
Note for OpenSuse users: remember to open the ports in your firewall. The port range is 1714-1764 for both TCP and UDP.
I'm not an OpenSuse user, but nevertheless this is the magic hint !
Now I'm a happy user of KDEConnect, I like the notifications service, and also used extensively the "share clipboard" feature.
I just wish they could give a hint about the firewall ports, either in the app or in the KDE settings screen on the PC !