I don’t think you’ll have many problems with those packages unless they’re not on nixpkgs (if that’s the case you’ll have to make the package yourself) You also have to consider that NixOS works differently than most Linux distros: the filesystem is different so installing apps through any other means other than nix will be difficult if not compromising reproducibility of the system (the main promise of NixOS) I’m not sure how compatible flatpak is with NixOS too. KDE does work well though. I overall wouldn’t recommend this OS to anyone who isn’t willing to fight the terminal and read the docs furiously (for around 2 days, after that you’ll stabilize and be grateful you did it). NixOS is a wonderful operating system. Works marvels.