How to setup alerts when PHP is updated by AWS

If you're referring to Elastic Beanstalk (?), you can define a maintenance window for platform updates where you can also configure to receive notification when an upgrade is executed. The following pages in the documentation provide information on these features:

• https://docs.aws.amazon.com/elasticbeanstalk/latest/dg/environment-platform-update-managed.html
• https://docs.aws.amazon.com/elasticbeanstalk/latest/dg/AWSHowTo.eventbridge.html

Please note that this is applicable only if Managed Updates are enabled. Notifications for the event that an update for the platform is available are currently not supported.