Apex domains cannot have CNAME records.
Question and response
Question
dig amsterdam. NS
Answer
amsterdam. 5 NS ns4.dns.amsterdam.
amsterdam. 5 NS ns3.dns.amsterdam.
amsterdam. 5 NS ns1.dns.amsterdam.
Authority
The response has no authority records.
Additional
ns1.dns.amsterdam. 62648 A 194.0.28.4
ns3.dns.amsterdam. 62648 A 194.0.25.26
ns4.dns.amsterdam. 62648 A 185.159.199.202
ns1.dns.amsterdam. 62648 AAAA 2001:678:2c:0:194:0:28:4
ns3.dns.amsterdam. 62648 AAAA 2001:678:20:0:0:0:0:26
ns4.dns.amsterdam. 62648 AAAA 2620:10a:80ac:0:0:0:0:202
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0