Not even then. For example the biggest Linux distribution in use is Ubuntu, and it doesn’t have flatpak built in. So even if a flatpak of an app is available, a user of Ubuntu would have to already understand what a flatpak is, and already know that it would make the app installable on Ubuntu, and know that flatpak itself can be installed separately, and know how to use a different install method already just to get the flatpak system onto their computer in the first place