@gamingonlinux The sandbox of a flatpak is the same on all distributions, unlike a snap¹. In addition, the snapcraft.io backend is proprietary (unlike Flathub), so this format will never be adopted by all distributions. If they really want to be cross-platform, they should start by working on these two points.

¹ https://en.wikipedia.org/wiki/Snap_(software) search for AppArmor