Apex domains cannot have CNAME records.
Question and response
Question
dig tektonic.pc2linux.com. NS
Answer
tektonic.pc2linux.com. 5 NS tektonic-cloud6.pc2linux.com.
tektonic.pc2linux.com. 5 NS do6.pc2linux.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0