Except that some things will remain scarce.
There's limited amounts of land to put mansions on. There's limited amounts of mass to work with. There's limited numbers of other people to work with.
In Star Trek (TOS), there were a very limited number of starships, suggesting that they weren't free. (I never did understand the difference between a starship, like the Enterprise, and a spaceship capable of interstellar travel, usually offscreen.) The Enterprise was constantly running into people who didn't have unlimited material wealth. Cyrano Jones was negotiating tribble prices in "The Trouble with Tribbles", and seemed anxious to get free drinks, suggesting that alcohol was at least treated as a scarce resource. No Enterprise crew member worried about money, but they had demanding jobs that took them anywhere in the galaxy whether they wanted to or not, and could (and sometimes did) get them killed.
Moreover, we are in what would look like a post-scarcity economy to previous eras. If we had the political will, and wanted it so, we could easily provide everybody with shelter, food, medical care, etc., that would look almost miraculous to anybody from the Renaissance. We could give everybody a sword as good as anything a king had in those days, no problem. Most of our poor people live much better than 99% of medieval people. About the only advantage a 14th-century king would have over me was the ability to boss people around.
The only way we could have a true post-scarcity economy would be if we were able to manufacture robots for any need (including therapy, sex, and general companionship), and rationed out scarce things like land without money.