File namespace.yaml should be moved to directory config/default. After deploying secret and ext-postgres-operator (tag 2.0.0) with kustomize:

kubectl kustomize config/default/ | kubectl apply -f -

the following error occurs:

Error: failed to create containerd task: failed to create shim task: OCI runtime create failed: runc create failed: unable to start container process: error during container init: exec: "postgres-operator": executable file not found in $PATH

The problem seems to be solved after removing spec.template.spec.containers[0].command from ext-postgres-operator deployment manifest.