Apex domains cannot have CNAME records.
Question and response
Question
dig xta.cat. NS
Answer
xta.cat. 5 NS ns2.xta.cat.
xta.cat. 5 NS ns1.xta.cat.
Authority
The response has no authority records.
Additional
ns1.xta.cat. 5 A 185.73.168.3
ns2.xta.cat. 5 A 185.73.168.4
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0