On the node with Horizon service
Ensure that the horizon container is in the running state. Please note that "Horizon" container is replaced with NetBackup for OpenStack Horizon container. This container has the latest OpenStack horizon + NetBackup for OpenStack's horizon plugin.
[root@overcloud-controller-0 heat-admin]# podman ps | grep horizon 094971d0f5a9 rhosptrainqa.ctlplane.localdomain: 8787/nbos-horizon-plugin:9.0-rhosp16.1 kolla_start 5 days ago Up 5 days ago horizon