By default, Strapi will be available on an auto-generated domain via http protocol.
To configure a custom domain you would need to do the following:
To enter a custom domain, go to the environment, in Resources, click the AppRunner resource, then in Resource Settings find the DomainName parameter.
To create an SSL certificate follow the How to create SSL certificate guide.
Make sure that the domain name specified in the certificate matches the domain name provided in the AppRunner resource from the previous step.
Once you have your issued SSL certificate through AWS Certificate Manager you just need to copy the certificate ARN and past it in the AppRunner resource CertificateArn parameter (view image above).
Click on the Save button to only save these changes, or select the Save and Deploy button to apply the changes in the cloud.
In the AppRunner resource > Overview tab, under Resource Outputs, you should see the value of the CNAME parameter. Copy this value and add it as a CNAME record in your DNS provider.