With Lets Encrypt no longer generating Expiration Notification Emails, here's a couple of ways you can replace the service with something you can build yourself. Use AWS Free tier resources to check your certificates. Learn how to automate certificate expiration checking.

Certificates will no longer use Whois based information for Domain Control Validation

Finding the owner of expiring certificates used for IAM Roles Anywhere.

Deploying a root and intermediate CA using CFSSL and Ansible

Using a Self Signed CA with K8s and updating trusted CAs on Centos