I almost entirely listen to music as a means to focus; someone singing in a language I understand (French or English) will distract me too much and I will probably skip it, so I don't know much French singers. I do however know some French artists in general if you're fine with stretching the question to those who just make music. I regularly listen to Carpenter Brut, HUBRID, Speed Machine, M.A.D.E.S., and other synthwave artists on SoundCloud. I would say of the artists that I am 100% sure are French then Carpenter Brut is my favorite.