You can install nix. Does not give you sandboxes like flatpak unless combined with other tools like firejail or nixos-shell, but at least nixpkgs-unstable is one of the most up-to-date package managers out there.
snaps are the one I'm most familiar with, which provides sandboxing wherever possible, automatic updates, and a permissions system where I can do things like deny Firefox access to my webcam. And is available on a number of Linux distributions.