If you use an Arch-based distro, it's available in the Arch User Repository (AUR) [1]. With Aura [2], installation is as simple as:
aura -A radarr
Yes, you need to use the CLI to run that, but it's trivial to do so and a real package management system brings many advantages over exe installers. The AUR, inspired by BSD's Ports, is one of the major advantages of Arch. It's very rare to find a package that isn't supported.
Manjaro comes with a GUI for Pacman and after enabling AUR (and clicking the "yes I know this will probably break my machine" button) it simply shows up in the list of installable software.
That said, Radarr, being written in dotnet, should be able to package a single executable you can just click, and that process should be even easier with the upcoming dotnet release.
[1] - https://aur.archlinux.org/packages/radarr
[2] - https://github.com/fosskers/aura