The screenshot you posted shows nothing for 21, 22, 23. It also shows nothing for every Tuesday and Wednesday in September. Did you notice that? I don't know what booking site that is but it does not appear to be the Air France site.
Did you check Air France's own website to see what it showed? Kubrick indicates that it shows available on the Air France site.
There are many reasons why there might actually be no availability, not just group bookings. You have no way of knowing if that is the case or not but Air France does.