Apex domains cannot have CNAME records.
Question and response
Question
dig v6.fi-hel2.upcloud.host. NS
Answer
v6.fi-hel2.upcloud.host. 5 NS ns1-de.upcloud.com.
v6.fi-hel2.upcloud.host. 5 NS ns1-fi.upcloud.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0