Memes

the Culture series is the only one i've ever read (some of) that explored around the edges of an advanced, actually fully developed communist society. and it's not even the future, nor Earth (it mostly takes place in the past) (obviously less grounded it's just Star Trek with coherant physics and at a higher power level). definately utopian, or more a guy who watched star trek as a young adult and said "what if i wrote my own Star Trek but the Federation is actually full communist at every level".

for hardish sci/fi:

the Mars Trilogy by demsoc Kim Stanley Robinson ends with a global and then interplanetary socialist revolution but has some weird tropes and relies on too much hand waving. not utopian at least, there is a violent revolution and multiple competing ideologies/tendencies that cobbles together green socialism, market socialism, anarchism, and vanguardism. but unfortunately the revolution on Earth is skipped over.

it sucks because the story beat of global megacorps with domains the size of nations fighting a conventional/cyber war with an alliance of newly formed socialist republics and mega-cooperatives sounds fucking awesome

there's optimism but you have to grind through some forgettable characters.

the spiritual successor he wrote, 2312, took place in a socialist Sol system, but also more early stage market socialist with libertarian socialist elements. dunno i didn't like it only got a chapter in.