Unlike Prometheus and Thanos components, the cluster admins can't configure the Alertmanager's log level. It should be possible to do this in the CMO configmap:

apiVersion: v1
kind: ConfigMap
metadata:
  name: cluster-monitoring-config
  namespace: openshift-monitoring
data:
  config.yaml: |-
    alertmanagerMain:
      # default is info
      logLevel: debug

DoD

• cluster admins can set the Alertmanager's log level in the cluster-monitoring-operator configmap.