Get all Deployments referencing given ConfigMap by the ConfigMap's name
You can use kubectl get -o json and parse the output using jq to iterate over the deployments, matching any desired configMapKeyRef.name and returning a uniq list of deployments.
This should work:
kubectl get deployments --all-namespaces -o json | jq -r '.items | map(select(.spec.template.spec.containers[]?.env[]?.valueFrom.configMapKeyRef.name == &quot;london-tz-config&quot; ) | .metadata.name) | .[]' | uniq