Even with a post-scarcity society with nigh-magical technology underpinning it, it's not unreasonable that there'd be some form of currency as certain things - like land, for instance - aren't reproducible regardless. Presumably Picard owns his family vineyard, but how that works in terms of the Federation's economy is hazy at best. Though it can be reasonably assumed based on Trek dogma that Picard's not producing wine for the ultimate goal of acquiring further wealth but rather for the very pleasure of the work itself. Much like Ben Sisko's father presumably cooks Cajun food out of his own love for the craft but how his restaurant works in the broader Federation economy I have genuinely no idea.

Although, from a canonical standpoint, the only power which has no stated monetary system is the Federation. Most of what we've seen thus far has been outside of that, which has generally been presented to be a more-or-less contemporary market economy.

There's also the even more nebulous territory of Federation citizens possessing local currency, like on DS9. No idea how that works, or in the case of this show with Picard, what wealth is actually in his name.