Snap and Flatpak are both (theoretically) distro agnostic. That's their entire point of existence, to solve scenario three of your list. Yes, Fedora defaults t

Snap and Flatpak are both (theoretically) distro agnostic. That's their entire point of existence, to solve scenario three of your list. Yes, Fedora defaults to and prefers Flatpak and Ubuntu defaults to and prefers Snap, but you can install either on either distro and it should Just Work. In which case, distro-specific differences are an even further moot point.