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