Avril et le monde truqué (April and the extraordinary world, 2015)?
In 1941, the world is radically different from the one we know from history books. Geopolitics has developed strangely: Napoleon V rules France and, for the last 70 years, scholars have been mysteriously disappearing, depriving mankind of their inventions. Without radio, television, electricity, aviation, and the combustion engine, the world is mired in outdated technology, dozing in the previous century's knowhow dominated by coal and steam. In this bizarre universe, Avril (Marion Cotillard), a teenage girl, Darwin (Philippe Katerine), her talking cat, Pops (Jean Rochefort), her grandfather, and Julius (Marc-André Grondin), a young scoundrel and police informer, go off in search of Avril's parents, two of the missing scientists. The quartet will face many dangers and mysteries in this strange new Rigged World.
Found with the Google query
film francais chat qui parle nuage noir scientifiques (
french movie talking cat black cloud scientists) which returned the movie's page on Allociné, the main French site about cinema.