The documentation stated that ELB couldn't change the healthy response code. However, since both NLB and ALB now support 4xx codes, I've removed this example from the description.

ALB

https://docs.aws.amazon.com/elasticloadbalancing/latest/application/target-group-health-checks.html
Matcher: If the protocol version is HTTP/1.1 or HTTP/2, the possible values are from 200 to 499.

NLB

https://docs.aws.amazon.com/elasticloadbalancing/latest/network/target-group-health-checks.html
Matcher: [HTTP/HTTPS health checks] The HTTP codes to use when checking for a successful response from a target. The range is 200 to 599. The default is 200-399.

NLB support for this feature was added in November 2022

https://aws.amazon.com/about-aws/whats-new/2022/11/elastic-load-balancing-capabilities-application-availability/
Network Load Balancer (NLB) Health Check Improvements: NLB allows customers to define health check intervals, specify HTTP response codes that determine target health, and configure the number of consecutive health check responses before a target is either health or unhealthy. For details, see the NLB health check documentation here.