Apex domains cannot have CNAME records.
Question and response
Question
dig 163.85.in-addr.arpa. NS
Answer
163.85.in-addr.arpa. 3 NS dns02.cetin.cz.
163.85.in-addr.arpa. 3 NS dns01.cetin.cz.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0