Apex domains cannot have CNAME records.
Question and response
Question
dig olimp-uac.ua. NS
Answer
olimp-uac.ua. 5 NS ns19.o-net.com.ua.
olimp-uac.ua. 5 NS ns21.o-net.com.ua.
Authority
The response has no authority records.
Additional
ns19.o-net.com.ua. 5 A 185.102.184.19
ns21.o-net.com.ua. 5 A 185.102.184.21
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0