When setting the environment variable OPENSHIFT_INSTALL_SKIP_PREFLIGHT_VALIDATIONS=1, the install process is still being aborted when the Control plane replicas are set to a number different than 3.
The install-config validation is a "static check" and not a "pre-flight check" and as such, it can't be skipped with the same environment variable. Note that with https://github.com/openshift/installer/pull/4672 , the validation only aborts the installation when "replicas > 3" (it was "replicas != 3").