If you were to look out for what sci-fi/futuristic communism looks like it most certainly converges into some sort of world government, at the very least with a diminished role of nation states as the concept we have today.

It is literaly impossible to look after the resources in this planet otherwise while still claiming to do what is best for humanity as a whole. This is one of the explicit goals of communism.

Obviously that doesn't mean some handful of people in San Francisco or Paris gets to decide everything for 8 billion people, but rather some degree of autonomy for obvious reasons. This is why so many people want to ahve their take on how it would look like.

If you want to be technical about it Star Trek imo sort of manages to at least be coherent about this because they recognize that scarcity(material conditions) is one if not the most important thing, therefore by waving the magic wand and solving scarcity you can go around the global resources management problem entirely and just pretend life is so good it doesn't matter if you have a local government or not, you know considering you can instantly go from one side of the planet to the other via a transporter etc.

Star Trek is a world without boundaries but I'm pretty sure this is not a capitalist analogy since I believe people can just live anywhere they want(on or off world), you know free movement of labor is anti-capitalist.

Anyway this end of history thing doesn't look like anything I just talked about unless you base your argument on dictionary definition of words only.