Apex domains cannot have CNAME records.
Question and response
Question
dig doop.fi. NS
Answer
doop.fi. 5 NS ben.ns.cloudflare.com.
doop.fi. 5 NS joan.ns.cloudflare.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0