My intention wasn’t to misinterpret your post; I genuinely thought you were asking for help using flatpaks without the terminal on your Xubuntu setup. As for the topic of this thread, as a Bluefin user, I’d argue that we’re coming very close of being able to daily drive Linux without ever opening the terminal at all.

(also, the Flathub instructions page you’ve linked on your post do mention installing gnome-software)

Flatpak is not a store, it’s a package format. Mint has a built-in “Software Manager” GUI app that allows you to browse Flathub and install flatpaks from there. On Xubuntu, I guess you’ll need to install gnome-software or Bazaar, or just the flatpak package if you don’t care about using a GUI