Apex domains cannot have CNAME records.
Question and response
Question
dig univmed.fr. NS
Answer
univmed.fr. 5 NS ns2.univmed.fr.
univmed.fr. 5 NS nsamu.u-ga.fr.
univmed.fr. 5 NS ns1.univmed.fr.
Authority
The response has no authority records.
Additional
ns1.univmed.fr. 5 A 139.124.1.1
ns2.univmed.fr. 5 A 139.124.196.2
ns1.univmed.fr. 5 AAAA 2001:660:5402:801:0:0:0:1
ns2.univmed.fr. 5 AAAA 2001:660:5403:f201:0:0:0:2
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0