Theres a whole alien race, The Ferengi, that are obsessed with something called latinum and getting as much as possible because it can’t be replicated. Other than that, it has no other useful purpose. You could replicate anything you want for free or ypu could get some platinum and go to a Ferengi bar and pay someone else to replicate it for you.

So basically yeah, Ferengi are also post-scarcity but since they are the capitalist caricatures of the show they have random substance xyz so they can still have a reason for rich and poor to exist.