What is the name of the domain?
example.com
What is the issue you’re encountering
Emails sent by Cloudflare with the purpose of validating actions, such as adding an address to Email routing or validating an address for Cloudflare One’s Email OTP authentication, lack TLSv1.3 support. These emails are sent using sparkpostmail.com as *@notify.cloudflare.com. As I’m not myself a customer of Sparkpost I request Cloudflare reaches out to Sparkpost aka Bird to see if they could enable TLSv1.3 for their MTA responsible for Cloudflare emails.