Apex domains cannot have CNAME records.
Question and response
Question
dig dns.build-ovh.net. NS
Answer
dns.build-ovh.net. 5 NS ns107.ovh.net.
dns.build-ovh.net. 5 NS dns107.ovh.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0