Apex domains cannot have CNAME records.
Question and response
Question
dig mailit.app. NS
Answer
mailit.app. 4 NS ns1.first-ns.de.
mailit.app. 4 NS robotns3.second-ns.com.
mailit.app. 4 NS robotns2.second-ns.de.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0