https://docs.redhat.com/en/documentation/red_hat_openstack_services_on_openshift/18.0/html-single/deploying_rhoso_at_scale/index#con_rhoso-deployment-configurations_best-practices-for-deploying-rhoso-at-scale

Section: Improve instance distribution across Compute

Set the value of the NovaSchedulerShuffleBestSameWeighedHosts parameter to true.

This seems to be old tripleo parameter.

In 18.0 you need to use the OpenStackControlPlane CR to set the nova-scheduler config to enable, [filter_scheduler]shuffle_best_same_weighed_hosts