To ignore application 4xx errors when determining your environment's health. we can simply edit EB health rule that ignores 400-499 HTTP status codes when alerting if your environment instances are having trouble.

It is common for applications to receive many 4xx errors, for example, due to:

Client's API integrations using invalid credentials. Client-side test tools. Broken links that create 404 responses.

To configure HTTP 4xx status code checking using the Elastic Beanstalk console Open the Elastic Beanstalk console, and in the Regions list, select your AWS Region.

In the navigation pane, choose Environments, and then choose the name of your environment from the list.

In the navigation pane, choose Configuration.

In the Monitoring configuration category, choose Edit.

Under Health monitoring rule customization, Activate the Ignore options.

To save the changes choose Apply at the bottom of the page.

This will ignore Http4xx request.

follow this docs for better understanding.... https://docs.aws.amazon.com/elasticbeanstalk/latest/dg/health-enhanced-rules.html