Apex domains cannot have CNAME records.
Question and response
Question
dig institut-kerhuon.com. NS
Answer
institut-kerhuon.com. 1 NS ns-695.awsdns-22.net.
institut-kerhuon.com. 1 NS ns-573.awsdns-07.net.
institut-kerhuon.com. 1 NS ns-193.awsdns-24.com.
institut-kerhuon.com. 1 NS ns-1827.awsdns-36.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0