Apex domains cannot have CNAME records.
Question and response
Question
dig lajsinet-ip.cz. NS
Answer
lajsinet-ip.cz. 5 NS ns1.lajsinet-ip.cz.
lajsinet-ip.cz. 5 NS ns2.lajsinet-ip.cz.
Authority
The response has no authority records.
Additional
ns1.lajsinet-ip.cz. 5 A 185.211.109.77
ns2.lajsinet-ip.cz. 5 A 185.211.109.78
ns1.lajsinet-ip.cz. 5 AAAA 2a0b:6440:1:100:10:10:10:77
ns2.lajsinet-ip.cz. 5 AAAA 2a0b:6440:1:100:10:10:10:78
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0