If Cloudflare is providing authoritative DNS for your domain, Cloudflare will issue a backup Universal SSL certificate for every standard Universal certificate issued.
Backup certificates are wrapped with a different private key and issued from a different Certificate Authority — either Google Trust Services or Sectigo — than your domain’s primary Universal SSL certificate.
These backup certificates are not normally deployed, but they will be deployed automatically by Cloudflare in the event of a certificate revocation or key compromise.
For additional details, refer to the introductory blog post.
Can opt out?