> The problem is that some software authors, like Radarr's, don't believe in the model.
And I don't really blame them. People love to pimp Flatpak and Snap, but nobody ever likes to talk about the issues that portals cause, the horrible rendering issues it lugs along, the lack of molecularity constantly breaking things on xorg/Wayland, the DBUS issues, the extremely esoteric configuration options, the auto-updating (!!!) and so on and so forth.
Apple makes this work because they have hundreds of billions of dollars they can divert to R&D. Linux gets the short end of the stick because it's a game of chicken-and-egg: none of the developers want to work on Flatpak because none of the packagers want to provide packages for it because Flatpak has hundreds of outstanding bugs and an entire community of people like me who remember being promised bigger and better things on Linux, only to have them fall through the ground not even halfway into development.
Simplicity is key. Flatpak, Snap, and all of it's ilk are not simple, which is why it's no surprise that their development is lethargic and adoption is, kindly put, sluggish.