Apex domains cannot have CNAME records.
Question and response
Question
dig sfera.net. NS
Answer
sfera.net. 5 NS thunder.sfera.net.
sfera.net. 5 NS dns.sfera.net.
Authority
The response has no authority records.
Additional
dns.sfera.net. 5 A 80.91.49.210
thunder.sfera.net. 5 A 80.91.50.194
dns.sfera.net. 5 AAAA 2a02:6000:53:0:0:0:0:53
thunder.sfera.net. 5 AAAA 2a02:6000:53:1:0:0:0:53
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0