I wanted to make a suggestion to improve the installation experience from flathub.
As opposed to downloading flatpak ref files, one could also use appstream URIs, which can be opened by many software management programs (e.g. GNOME Software Center, Discover, etc.).
This would automatically open the software (or let the user choose, which software to use) as opposed to first downloading a file, which has to be opened with the correct software.
There is even an add-on for Firefox now to replace the installation button: GitHub - CleoMenezesJr/flatline: Open apps directly in GNOME Software by clicking Install from Flathub and apps.gnome.. I think it is much more intuitive and also quicker. But I’m not a fan of having add-ons for such simple tasks, as they are always a security concern.
Maybe you could also add both possibilities by adding a second button as suggested by FreeDesktop: URI Handler | AppStream | AppStream 0.15.
I’m not sure if that was already discussed, but I didn’t find any topic in this forum.
For any more questions, I’m happy to give more information.