Apex domains cannot have CNAME records.
Question and response
Question
dig si. NS
Answer
si. 5 NS k.dns.si.
si. 5 NS b.dns.si.
si. 5 NS f.dns.si.
si. 5 NS h.dns.si.
si. 5 NS i.dns.si.
si. 5 NS l.dns.si.
Authority
The response has no authority records.
Additional
b.dns.si. 172152 A 153.5.81.140
f.dns.si. 162558 A 194.146.106.62
h.dns.si. 162056 A 204.61.216.54
i.dns.si. 172136 A 194.0.25.22
k.dns.si. 162056 A 185.159.197.11
l.dns.si. 162056 A 185.159.198.11
b.dns.si. 172152 AAAA 2001:1470:8000:53:0:0:0:44
f.dns.si. 162558 AAAA 2001:67c:1010:15:0:0:0:53
h.dns.si. 162056 AAAA 2001:500:14:6054:ad:0:0:1
i.dns.si. 172136 AAAA 2001:678:20:0:0:0:0:22
k.dns.si. 162056 AAAA 2620:10a:80aa:0:0:0:0:11
l.dns.si. 162056 AAAA 2620:10a:80ab:0:0:0:0:11
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0