I have KDE Connect on my laptop (nix), my desktop (Fedora), my Phone (android), and my Steamdeck (SteamOS). Before I started using NixOS on my laptop I had fedora too. And KDE connect worked between all 4 of my machines.
Now since I installed Nix on my laptop the laptop and the Fedora desktop both connect to the Phone and the Steamdeck, but can’t connect to each other.
I have ruled out a port issue since it works with the other machines, and I think it is an error in my Nix since it is the element that changed.