As shown in this run of OpenShift conformance tests, the test " Cluster scoped load balancer healthcheck port and path should be 10256/healthz" fails:

{  fail [github.com/openshift/origin/test/extended/cloud_controller_manager/ccm.go:125]: Expected
    <string>: TCP:31611
to equal
    <string>: HTTP:10256/healthz
Ginkgo exit error 1: exit with code 1} 

In AWS, LoadBalancer services are expected to create AWS LoadBalancers with:

Ping protocol: HTTP

Ping port: 10256

Ping path: healthz

These values match the kube-proxy running on each node. This change was brought in https://github.com/openshift/cluster-cloud-controller-manager-operator/pull/383 by settting the shared mode for ClusterServiceLoadBalancerHealthProbeMode config element. This change was also backported to 4.19 but not to 4.18. Version 4.18 can't use this flag so it sets the protocol/port in a different way.

HostedControlPlane doesn't configure the probe mode as can be seen here (CPO v2) and here(CPO v1) so it uses the default mode ServiceNodePort. The ClusterServiceLoadBalancerHealthProbeMode config element should be set here.

Link to slack discussion