Apex domains cannot have CNAME records.
Question and response
Question
dig ip-145-239-158.eu. NS
Answer
ip-145-239-158.eu. 4 NS dns103.ovh.net.
ip-145-239-158.eu. 4 NS ns103.ovh.net.
Authority
The response has no authority records.
Additional
ns103.ovh.net. 3 A 5.135.54.65
dns103.ovh.net. 3 A 5.196.39.89
ns103.ovh.net. 3 AAAA 2001:41d0:b00:f700:0:0:0:2
dns103.ovh.net. 3 AAAA 2001:41d0:d00:fd00:0:0:0:2
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0