Apex domains cannot have CNAME records.
Question and response
Question
dig nextron.ch. NS
Answer
nextron.ch. 5 NS dns2.nextron.ch.
nextron.ch. 5 NS dns.nextron.ch.
nextron.ch. 5 NS dns3.nextron.ch.
Authority
The response has no authority records.
Additional
dns.nextron.ch. 5 A 193.108.137.2
dns2.nextron.ch. 5 A 193.108.137.3
dns3.nextron.ch. 5 A 31.171.251.198
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0