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