Apex domains cannot have CNAME records.
Question and response
Question
dig oxem20.net. NS
Answer
oxem20.net. 5 NS ns.oxem20.net.
oxem20.net. 5 NS sdns2.ovh.net.
Authority
The response has no authority records.
Additional
ns.oxem20.net. 5 A 91.121.45.191
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0