Its even worse when you force Firefox to use wayland its icon doesn't even show.
Edit: Oh since everyone now is confused; I only have the flatpak version of Firefox installed yet it doesn't use the pinned icon and doesn't even use the firefox icon under wayland at all.
Am a developer and I can very much agree on package managers have nasty configuration, but at the same time flatpak is the exact same thing. No different that any other package. Except now you have to learn yet another standard that's even less popular than major ones. You can even claim it's easier, but the fact remains it's not the defacto standard, so you still have to provide other packages as well as flatpak if you wish to do so.
flatpak isn't the same because you only have to learn one packaging format and can distribute to virtually any system out there. I really don't see why you'd also package for every distro individually then. Installing flatpak isn't that hard, it not being "the defacto standard" shouldn't be an issue.
If the system supports flatpak. Yes.
So basically the entire Linux desktop then.