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 on

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.