In french, we say "À tes souhaits" ou "À vos souhaits"

Dictionary link here

A quick googling of "bless you sneeze in french" reveals very easily the desired answer.

https://en.wikipedia.org/wiki/Response_to_sneezing

http://franconaija.blogspot.com/2015/05/what-to-say-in-french-when-someone.html

https://forum.wordreference.com/threads/god-bless-you-bless-you-sneezing.2058/

From the last link

1st sneeze : A tes/vos souhaits!

2nd sneeze : A tes/vos amours! (que
les tiennes/vôtres durent toujours)

3rd sneeze : A tes/vos aïeux!

4th
sneeze : Crève!

https://www.quora.com/How-do-you-say-bless-you-in-French-when-someone-sneezes