Apex domains cannot have CNAME records.
Question and response
Question
dig imshealth.com. NS
Answer
imshealth.com. 4 NS ns2.iqvia.com.
imshealth.com. 4 NS ns1.iqvia.com.
imshealth.com. 4 NS ns4.iqvia.com.
imshealth.com. 4 NS ns3.iqvia.com.
Authority
The response has no authority records.
Additional
ns1.iqvia.com. 4 A 162.44.245.2
ns2.iqvia.com. 4 A 162.44.221.241
ns3.iqvia.com. 4 A 162.44.225.5
ns4.iqvia.com. 4 A 162.44.225.6
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0