Apex domains cannot have CNAME records.
Question and response
Question
dig mgcloud.fr. NS
Answer
mgcloud.fr. 2 NS dns112.ovh.net.
mgcloud.fr. 2 NS ns112.ovh.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0