I wish we lived in a post-scarcity Star Trek world where there’s no money except there is but not in the Federation except when it IS in the Federation and no one has any needs except when they do.
I'm glad there is no money in the Federation. Unless you count credits. Which are not money. Unless you use thousands of them to pay the Barzans. Or give them to Starfleet officers to buy things like tribbles and drinks at Quark's.
It still sort of makes sense, as others mentioned for working with non-federation entities. But the money-less thing makes more sense to me if you have replicators. The only "cost" there is the material you use for the replicator. So even if you had a money society, things --should-- be dirt cheap since most even outside the federation should have a replicator.
In some ways, I think it'd be harder to have a money and market system when replicators exist.
I assume replicators have some non-trivial energy debt, too. If my memory were better, I might even remember an episode where replicators couldn't be used because they were on backup power. Like, compared to warp, it's nothing, but if the warp core or main dilithium generators are offline, replicators don't work.
I know we're in tenforward, but another good post-scarcity-except-when-not is Iain Banks' Culture. Intelligences still trade, but it's more information/skillset/favors based.
Replicators being unusable because of power shortages was an early plot point in Voyager, and there are things that can't just be replicated since they often had to trade with friendly civilisations that they encountered.
Of course, the real answer is that they went with whatever rules suited the plot at the time, consistency be damned.
Oh! In so glad I got to be the one to introduce you to Banks!!
A couple of caveats:
There's no starting point, and few overlapping characters. Start anywhere.
Some people think some books are better than others (and some people have strong opinions about a couple of the books). There are a couple books in particular that are commonly considered the best, and the worst. Read at least two before giving up, just in case the first isn't your cup of tea.
Iain is dead; he passed away a few years ago at a relatively young age. He only wrote a dozen or so Culture novels, and there won't be any more (from him).
I went from liking him to him being one of my favorite authors over a period of a decade.
The novels really are all over the place. By the time I'd reached the end of his bibliography, I fell into a depression that there wouldn't be any more. While other authors were his peers and friends, and some are put in the same general "feel" category, he really was quite unique and I haven't yet found an author who could fill his shoes.
If you have time and interest, I'd suggest looking online at some fan sites suggesting entry points (and points to avoid starting with). All his books are good, but I do think a couple read better if you're generally familiar with his writing than as first reads.
I envy you; you're in for a treat. Banks was one of the greats.
You're right that there is no starting point, but I would still start with Consider Phlebas. It was the first novel, so it's a good jumping-in point in terms of being introduced to the basic concepts. It's also still my favorite of the novels.
I wish they'd explored this more in Voyager, as rationing their energy reserves was always a narrative tension throughout the series. It would have been interesting to explore a crew used to post-scarcity economics have to wrangle with switching to scarcity economics and all of the problems that come with it.