I use KDE and was able to migrate to 25.11 without issues.
I thought you had a conflict between networkmanager and systemd-networkd, but I can’t see you using the latter from the config except for the usage of useDHCP. If I were you I’d disable it. I’d also set systemd.services.NetworkManager-wait-online.enable = false to be extra sure.
But anyway we need more information: is networkmanager running as it should? Why does KDE crash? etc.
About dr konqi: it is unfortunately useless as it crashes if any dependency of a given program or gdb itself lacks a build id, which is the default for nix binaries.