When creating an external scan profile, you are now able to select the option of monitoring a domain or/and subdomains in CT Logs. Keyhub monitors all publicly available CT Log nodes from Google, Cloudflare, DigiCert, Sectigo etc. If a certificate with a required domain name is detected it is added to your inventory.
If you want to be notified when a new Pre-certificate or Certificate was detected in CT logs go to Settings >> Notifications and set up the alerting.
Note: this feature is available on all paid plans.