@DownPW no. It needs to be an A record. CNAME is canonical meaning that traffic sent to it will land up at your main nginx site. The A record will sent headers which nginx can use to route the traffic correctly.
CNAME records do not have this and will resolve to the underlying host which will cause you problems. Useful for WWW and non-WWW, but that’s about it.
Essentially, it’s an alias and not a record in it’s own right.