Apex domains cannot have CNAME records.
Question and response
Question
dig bortzmeyer.org. NS
Answer
bortzmeyer.org. 2 NS ns2.bortzmeyer.org.
bortzmeyer.org. 2 NS ns1.bortzmeyer.org.
bortzmeyer.org. 2 NS ns.eu.org.
bortzmeyer.org. 2 NS ns1.shaftinc.fr.
bortzmeyer.org. 2 NS ns4.bortzmeyer.org.
bortzmeyer.org. 2 NS ns-global.kjsl.com.
bortzmeyer.org. 2 NS ns2.shaftinc.fr.
Authority
The response has no authority records.
Additional
ns1.bortzmeyer.org. 2 A 80.77.95.49
ns2.bortzmeyer.org. 2 A 172.104.125.43
ns4.bortzmeyer.org. 2 A 92.243.4.211
ns1.bortzmeyer.org. 2 AAAA 2602:fbb1:1:245b:0:0:0:42
ns2.bortzmeyer.org. 2 AAAA 2400:8902:0:0:f03c:91ff:fe69:60d3
ns4.bortzmeyer.org. 2 AAAA 2001:4b98:dc0:41:216:3eff:fe27:3d3f
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0