Apex domains cannot have CNAME records.
Question and response
Question
dig vuurwerk.nl. NS
Answer
vuurwerk.nl. 5 NS anahi.ns.cloudflare.com.
vuurwerk.nl. 5 NS konnor.ns.cloudflare.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0