As per doc  :  https://docs.openshift.com/container-platform/4.17/observability/cluster_observability_operator/cluster-observability-operator-overview.html#advantages-of-using-cluster-observability-operator_cluster_observability_operator_overview

The COO can create a monitoring stack per user namespace. You can also deploy multiple stacks per namespace or a single stack for multiple namespaces.  

We already have example of how to create MonitoringStack for specific project : https://docs.openshift.com/container-platform/4.17/observability/cluster_observability_operator/configuring-the-cluster-observability-operator-to-monitor-a-service.html

Need a doc with steps to use a single "MonitoringStack" for multiple projects.