guillaumeC In general yes. Every European IBAN should be fully usable throughout the whole EU according to the law. Not accepting any kind of German IBAN (including bunq's) in France would therefore not be allowed. More info: https://together.bunq.com/d/23003
Of course, some employers or institutions might not care about the law and you will experience IBAN discrimination regardless. Nothing really you can do except to try it out. That's also the reason for bunq offering French and German IBANs in the first place... otherwise there wouldn't be a reason why we couldn't use Dutch IBANs in every EU country.