Apex domains cannot have CNAME records.
Question and response
Question
dig server.eu. NS
Answer
server.eu. 2 NS ns1.server.eu.
server.eu. 2 NS ns.coredns.org.
server.eu. 2 NS ns2.server.eu.
Authority
The response has no authority records.
Additional
ns1.server.eu. 2 A 77.95.248.206
ns2.server.eu. 2 A 85.119.243.5
ns1.server.eu. 2 AAAA 2a00:1478:20:f:8:772:0:1
ns2.server.eu. 2 AAAA 2a00:e760:100:f:8:1113:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0