What is the authorized length of stay in France?
According to article 21 of the Schengen Agreement, a third-country national in possession of a valid residence permit issued by a Schengen Member State may travel freely within the territory of other Member States for a period not exceeding 90 days in any 180-day period, including France, subject to compliance with the conditions set out in this convention and in Regulations (EU) No. 265/2010 of the European Parliament and of the Council of March 25, 2010, No. 610/2013 of the European Parliament and of the Council of June 26, 2013 and No. 2016/399 of the European Parliament and of the Council of March 9, 2016.
Consequently, and unless one of these conditions is not met, the prefect cannot legally oblige a third-country national with a residence permit issued by a Schengen State to leave French territory less than 90 days after entering France.
It seems to us that this authorization must be cumulative with the rights granted to third-country nationals authorized to stay in France for 90 days without an entry visa: the case of American nationals, for example.
French Council of State, February 4, 2021, n° 436109
LexCase avocats, Immigration, Schengen