I just want to point out that yes, there are post-scarcity sci-fi settings and yes, post-scarcity societies can support a post-capitalism and thus post-currency 'pseudo-economy' in which there is little need for trade. And yes, in such a society energy and 'minerals' (building components) would be the critical pieces of such an economy, as together they can fabricate anything else that might be of value.
However,
1) Post-scarcity does not mean that the government and economy would necessarily change to do away with capitalism, and indeed, the government types don't seem to imply that post-capitalism is an innate feature of all governments. Even in Star Trek, not every society is post-capitalism even though every society is basically post-scarcity thanks to widespread technology. Stellaris's economy system (if indeed it does reflect a post-scarcity galaxy) doesn't support any sci-fi setting I'm familiar with, because most settings acknowledge that post-scarcity doesn't automatically result in universal post-capitalism principles. Rather, those settings are diverse.
2) It's not really clear that Stellaris is actually post-scarcity. True, energy+minerals fits the mold, but aside from that, the fact that planets require farms seems to preclude post-scarcity altogether (you can't be a post-scarcity society if food is a scarce resource). Also, there is a distinct lack of writing or technologies that support the notion that this is the case, as far as I am aware.
It seems a lot more like people are using post-scarcity as a post-hoc justification for a pretty limited economy system which has extraordinarily few moving parts. I like Stellaris, but its economy needs improvement. If it is intended to be a post-scarcity world then fine, double-down on that and explore what that means for different kinds of governments and their people, because currently the game doesn't. Expand what 'minerals' means and make them a meaningful game mechanic in and of themselves.
But honestly, I'd like to see currency, because currency in some form makes sense in almost every society. How currency is used could be an interesting mechanic in and of itself - I'm not suggesting that currency should just be dumped in to take the place of some of what energy is doing, it should be an internal mechanism for growth and an indication of prosperity. Maybe it's even possible to advance into a post-scarcity, post-capitalism society, and have that be a thing that you can strive for. And if they get around to alien types that are intrinsically non-humanlike, such as hive-minds or cybernetics, then maybe they could exist outside of the normal structure of trade and exchange. But using post-scarcity as a justification for a simplistic economy system, I don't like it.