Apex domains cannot have CNAME records.
Question and response
Question
dig 158.166.83.in-addr.arpa. NS
Answer
158.166.83.in-addr.arpa. 5 NS ns2.infomaniak.ch.
158.166.83.in-addr.arpa. 5 NS ns1.infomaniak.ch.
Authority
The response has no authority records.
Additional
ns1.infomaniak.ch. 5 A 84.16.66.66
ns2.infomaniak.ch. 5 A 84.16.67.66
ns1.infomaniak.ch. 5 AAAA 2001:1600:0:aaaa:0:0:0:a
ns2.infomaniak.ch. 5 AAAA 2001:1600:0:aaaa:0:0:0:b
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0