Apex domains cannot have CNAME records.
Question and response
Question
dig server-online.org. NS
Answer
server-online.org. 5 NS nick.ns.cloudflare.com.
server-online.org. 5 NS gwen.ns.cloudflare.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0