Apex domains cannot have CNAME records.
Question and response
Question
dig buxoverflow.com. NS
Answer
buxoverflow.com. 3 NS ns-817.awsdns-38.net.
buxoverflow.com. 3 NS ns-67.awsdns-08.com.
buxoverflow.com. 3 NS ns-1506.awsdns-60.org.
buxoverflow.com. 3 NS ns-1211.awsdns-23.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0