Apex domains cannot have CNAME records.
Question and response
Question
dig sebian.fr. NS
Answer
sebian.fr. 4 NS ns16.ovh.net.
sebian.fr. 4 NS dns16.ovh.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0