I run antiX as my daily driver. I just used Synaptic Package Manager to access the antiX official repositories. I am presented with a list of well over 59,000 available packages that have been vetted and approved by the antiX development team. PPAs, AURs, and other private repositories probably contain packages that are not in the official distro repositories. However, I don’t think anybody can vouch for the quality of packages contained in those private repositories. Who knows how malware-ridden the packages in private repositories are.

There is a possibility that Flatpacks, AppImages, and Snaps also contain packages that are not in official distro repositories. However, the official distro repositories contain many packages that have yet to make it into these three “universal” packaging systems.

The “universal” packaging systems claim as an advantage over Package Managers the fact that they deliver complete applications that include all dependencies. When I install a package using Synaptic, it also pulls in and installs all the necessary dependencies. AFAIAC, the “universal” package systems have no advantage over Synaptic.

BTW – how can Flatpack, AppImage, and Snap be called “universal” if there are not compatible with each other? “Universal” means ‘understood by all’. They are not understood by each other. Snap and Flatpack are being used by the companies that developed them (Canonical and Red Hat respectively) to dominate and monopolize the package installation field.