A - it’s never really been socialism, they have currency.
B - they also have replicators, which drastically changes the economics. You don’t need most people to have jobs, most people don’t need jobs, most cool stuff (like star ship parts) can be had for free.
People join Star Fleet to have something to do. Kind of like signing on for colony ships only with central air.
Sure, replicators which replicate real things out of .... what? So there is an economy somewhere supporting that fantasy tech.
It’s fantasy. As is socialism. Except that in real practice, socialism is theft.