These kinds of super-general questions that try to box very powerful and flexible technologies into specific categories often don't really have a single useful answer, but more a series of more specific comparisons that can be useful in specific situations:
- Container ecosystems like Docker and Podman do package up executables and dependencies together... so yeah... they're definitely a useful format for delivering portable executables that can run on many distros. They're not the only option for that, though... flatpak, snap, appimage isn't popular for servers but it can be used that way.
- Docker and Podman aren't just images though. They provide runtime primitives for both sharing info across containers and for isolating containers from each other (and the host). Appimage doesn't do much at runtime. Flatpak and Snap do provide runtimes that do a lot of similar filesystem and maybe process isolation tricks but I don't think they provide the network namespacing that classic container runtimes provide.
All of which is to say... there's some overlap among the technologies you've described. Analyzing the tradeoffs between them is much eacher in the context of a specific use-case than the general case of "portable apps", which can mean very different things to different people.