Can I Set the Origin Server Address to a CNAME Record If I Use Cloud WAF?

Yes. If the IP address of the origin server is set to a CNAME record, additional DNS resolution is performed after a domain name is added. That is, the CNAME is resolved to an IP address first. DNS resolution increases the delay. Therefore, a public network IP address is recommended for the origin server.

For details, see Adding a Domain Name to WAF.