Apex domains cannot have CNAME records.
Question and response
Question
dig amplitut.de. NS
Answer
amplitut.de. 5 NS mask.amplitut.de.
amplitut.de. 5 NS ns.amplitut.de.
amplitut.de. 5 NS ns2.d-zone.ca.
amplitut.de. 5 NS boa.amplitut.de.
amplitut.de. 5 NS ns1.d-zone.ca.
Authority
The response has no authority records.
Additional
ns.amplitut.de. 5 A 91.223.231.146
boa.amplitut.de. 5 A 5.75.244.113
ns1.d-zone.ca. 5 A 162.219.54.2
ns2.d-zone.ca. 5 A 162.219.55.2
mask.amplitut.de. 5 A 161.129.68.111
ns.amplitut.de. 5 AAAA 2001:67c:8a4:5000:0:0:0:53
boa.amplitut.de. 5 AAAA 2a01:4f8:c012:1000:0:0:0:1
ns1.d-zone.ca. 5 AAAA 2620:10a:80eb:0:0:0:0:2
ns2.d-zone.ca. 5 AAAA 2620:10a:80ec:0:0:0:0:2
mask.amplitut.de. 5 AAAA 2604:a00:50:4e:216:3eff:fe2d:dab7
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0