Not everyone in France dresses well. I personally prefer the more eclectic style found in the UK.* But, the way I interpret French style is one that is natural, individual, and somewhat relaxed. Not too polished but well groomed and with an eye to the fit and cut of a garment. Hopefully not entirely comprised of all brand new, matched designer items simply bc then the clothes tend to overpower. Most guides to French style build on a limited classic capsule made of separates: good jeans; a jacket; a well cut dress; some accessories. I don’t wear denim as often, so I substitute charcoal gray pants or cargos.
I happen to love premier designer RTW, but I mix different seasons, past years, and sometimes add a more artisanal accessory. Sometimes I warehouse current season items in my own closet until the trend has passed. This summer, it’s a structured straw bag from a small company called Heimat Atlantica (I have no connection except as a satisfied customer, though I did meet the owner after buying two bags). i do happen to adore the cut of courrege pants, and they are a nice basis for this type of style. And, they are less expensive than premier designer ones. One doesnt need expensive designer clothing, but a good tailor helps.
ETA: * British style, in my layman, outsider opinion, is more about contrast, irony, and humor. i don’t really do ironic, humorous fashion very well, but I admire it. I interpret French fashion as too pretty and flattering to be ironic, but that’s JMO.