KDE Linux is an “immutable base OS” Linux distro created using Arch Linux packages, but it should not be considered an “Arch-based distro”; Arch is simply a means to an end, and KDE Linux doesn’t even ship with the pacman package manager.
KDE Linux leans on Systemd for a great deal of functionality. Updates are atomic and image-based, with the last 5 OS images cached on disk. Only the Wayland session is supported. Apps primarily come from Flatpak.
https://linux.kde.org/#what-kind-of-base-technology-does-kde-linux-use
They disagree with calling it arch based: