While I will admit that I haven't read about the earliest times of France, I will say this, I do not think that any Historian worth their salt would qualify a specific event or date would crown the establishment of a nation such as France for a variety of reasons.
First and foremost, what is France? While the current concept of France has a specific border with specific lines about citizenship, it was different even sixty years ago, there were many that saw Algeria as a part of mainland France. It was different a hundred years ago when France was rebuilding and just regained Alsace-Lorraine... and so on and so on. As such, the idea of France, just as with any nation, is always changing and morphing depending on the culture and events it experiences.
Second, when is France France? Even if we went as early as those in r/France, France is a fractured and rough concept that doesn't properly comes into light until the Hundred Years War, and even then... it weakens and is only reestablished by Louis XIV. Is William the Conqueror a Frenchman or a Norman? When did Burgundy lose it's identity? How did Brittany become less weird?
Third, what counts as French? Even if we determine France as a specific ethnic or linguistic concept, the former doesn't hold well as French ethnicities disappear by the mid 19th century and the French language doesn't become solidified by that time as well. While there are events that do establish these things (such as the French Revolution being a major part in the establishment of the French we know now), does this mean that the Gascon peasant isn't French because of his different French or different ethnicity?
Finally, what is France? Back to this question. Many nations are tied by a general narrative or concept that has lasted throughout their time. Britain has had a strong monarchy that slowly weakened but still serves as a representative; the United States is defined by it's short but impactful time in history... One thing that does come to mind is a short section where Alistair Horn describes his own study of French history.
>"Writing about the history of France has the elements of a love affair with an irresistible woman; inspiring in her beauty, often agonising and maddening, but always exciting, and from whom one escapes only to return again."
This short quite, while questionable in nature, I feel describes why it's impossible to define France, and therefore define when France starts. It is far from consistent (19th century France has no less than four serious revolutions and many minor revolts), experiencing a series of events that takes it from a fractured "feudal" Kingdom to the definition of Absolutism, to Revolution, Republics, Constitutional Monarchies, and then back to a Republic (and Fascist lapdog) that became the center of Culture to the entire world.
All of this to say, that France is far from any specific event or date.