Maybe it's just a me problem, but I always have had troubles getting KDE Connect connecting my phone to other devices than my desktop. My phone and laptop could both be connected to the same wifi and be within inches of each other but refuse to acknowledge their existence. But I have my phone on the other side of the world and I swear it'll be able to connect to my desktop with no problem.
KDE Connect is a pretty good program, but I can't recommend it because of the troubles I always have.
I had this too until I discovered my router doesn't allow communication between devices connected to the 5GHz band. 2.4GHz works fine so now I have everything connected to that
It's ability to connect your phone to your computer is honestly awful. It would be better if they just openly popped up a window and told you to pick the IP, but they even have to hide that and not support it on every platform.
My laptop's plugged in my phone's on a Wi-Fi network they're on different VLANs. They could let me search for it by DNS name. They could let me just use a couple of static IPs so when I go from home to work it could find it in either place.
If you have any equipment beyond a crappy one band ap, it's just going to fight you every time you want to use it.
I love the software, I love the plugins It's just too damn bad that You have to remember to screw with it every time you think you might want to use it.