KDE neon is described as 'Ubuntu-based Linux distribution that offers a stable and easy-to-use platform, featuring the latest KDE Plasma desktop and application releases' and is a popular Linux Distro in the os & utilities category. There are more than 100 alternatives to KDE neon for a variety of platforms, including Linux, Self-Hosted, BSD, Mac and Windows apps. The best KDE neon alternative is Linux Mint, which is both free and Open Source. Other great apps like KDE neon are Ubuntu, Debian, Fedora and Arch Linux.
Manjaro and KDE Neon are based on the Plasma desktop. Manjaro is a rolling distro so gets very quick updates, the moment new software versions are out. Neon gets this only for the Plasma desktop component. Otherwise, Neon is Ubuntu LTS under the hood.