linuxmemes

Usually people mean flatpak and other desktop-focused formats when talking about universal package formats.

Even docker images are usually built with traditionial package managers, except if they're built directly by Nix.

I agree that there won't be "the" package format, since they all have their tradeoffs. E.g. Nix updates need quite a bit of memory, so it isn't a good choice for resource constrained embedded use-cases.