Flathub aims to be the place to get and distribute apps for Linux. It is powered by Flatpak which allows Flathub apps to run on almost any Linux distribution.
How does it stack up against traditional package management and others like AUR and Nix?
Doesn't work properly, apps are bigger and don't always apply GTK themes. I also can't easily edit the desktop file to edit the icons. I therefore only use it as a backup when I can't find an app on the AUR or office repositories, which is very rare.
For editing desktop entries, copy it fron this strange directory ~/.local/share/flatpak/exports/share/applications/ to your normal ~/.local/share/applications which will always override the others.