Apex domains cannot have CNAME records.
Question and response
Question
dig T21V.RU. NS
Answer
t21v.ru. 5 NS ns1.t21v.ru.
t21v.ru. 5 NS ns2.t21v.ru.
Authority
The response has no authority records.
Additional
ns1.t21v.ru. 5 A 91.245.33.38
ns2.t21v.ru. 5 A 141.101.236.18
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0