Apex domains cannot have CNAME records.
Question and response
Question
dig cytadel.fr. NS
Answer
cytadel.fr. 5 NS zara.ns.cloudflare.com.
cytadel.fr. 5 NS jake.ns.cloudflare.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0