At the moment, new information is being published almost daily. However, these websites should have the latest updates.
Information from Remain in France
https://www.remaininfrance.fr/
Information from the French government:
https://www.brexit.gouv.fr/sites/brexit/accueil/vous-etes-britannique.html
Information from the British Embassy in Paris:
https://www.gov.uk/government/news/information-and-events-for-british-citizens-in-france
And practical advice and updates from the British Consular Services in France:
https://www.gov.uk/guidance/living-in-france
English-language newspaper The Connexion France:
https://www.connexionfrance.com/French-news/Brexit
British in France (representing Associations in France)
https://www.britishinfrance.com
News and Information from Remain in France, useful tips about French administration processes