You can read about it in English in a Reuters article signed by Elisabeth Pineau and Michel Rose, or in French in (among many other places) a Le Monde editorial (not behind a paywall).  But mostly you’ll read about how Macron’s strategy to win a symbolic victory over the established parties of the center-right and center-left has been “plunged into uncertainty.”  That doesn’t make for a very uplifting story.  You can test the argument Villani himself has put forward to motivate his candidacy

“Many complex problems will need to be worked out, which can be done by working together playing to our strengths,” Villani told supporters. “I’ve been tackling complex problems my whole life before entering politics.”

by substituting his fellow Fields medalists, one after another, for the “Lady Gaga of Mathematics”:  are you convinced?

His more relevant “strengths” can be read off the list of supporters who attended the announcement of his candidacy:

…nombre de ses soutiens sont à puiser chez les déçus de la “macronie”.

On y trouve le député Matthieu Orphelin, un proche de Nicolas Hulot qui a quitté le parti présidentiel en février, la députée Anne-Christine Lang, élue du 13e arrondissement, un ancien porte-parole de LaRem, Rayan Nezzar, et Paula Forteza, élue LaRem des Français de l’étranger.

(from the unsigned French Reuters article published on Mediapart but behind a paywall.)

The candidate Macron originally preferred has his own supporters:

Face à [Villani], Benjamin Griveaux peut compter sur l’appui du président de l’Assemblée nationale, Richard Ferrand, de Stanislas Guerini, de son ancien collègue Mounir Mahjoubi – ex-soutien de Cédric Villani – et de ministres comme Marlène Schiappa et Agnès Buzyn.

Meanwhile, the incumbent Socialist mayor Anne Hidalgo has yet to start her campaign for reelection, but her chances are looking considerably better since Macron’s movement split.  Here’s Hidalgo, looking very mayoral at a ceremony last year honoring the exiles of the Spanish Republic who played a crucial role in liberating Paris in 1944.

The Reuters article will tell you that this split

… could help Hidalgo win re-election, despite her own unpopularity due to the congested streets and polluted air of Paris.

This claim, which is typical of the English-language media, should not be taken at face value.  The bitterest attacks on Hidalgo have come from drivers, often from the wealthy western suburbs of Paris, who complain about her administration’s closure of parts of the city center to automobile traffic.  This policy has been promoted by her Green party allies (EELV — Europe Écologie les Verts) in the Paris city council.  Yannick Jadot, EELV’s candidate in the 2017 presidential election, has no problem with Hidalgo on that score:

“Le bilan d’Anne Hidalgo en matière d’écologie est celui des écologistes. Donc cette partie là, j’en suis très fier”, déclare Yannick Jadot.

Villani, meanwhile, announced that

he would be Paris’ first “truly environmentalist mayor”

But what does that mean?