This EPIC is the result of a Customer Interaction:

Is it possible to specify multiple clusters in a ClusterSelectors field?
According to https://github.com/stolostron/policy-generator-plugin/blob/ae7f23cf32f056670c3626d1a47962e08c6ed8b3/docs/policygenerator-reference.yaml#L116 you should be able to specify several selectors, but this works, for example, with lists ("-" in front of the key ) Not.
Are there any working examples?

It looks like the behavior of the generator is to create a MatchExpression for each key:value pair given:

spec:
  predicates:
  - requiredClusterSelector:
      labelSelector:
        matchExpressions:
        - key: cloud
          operator: In
          values:
          - red hat
        - key: this-other
          operator: In
          values:
          - label

If I'm not mistaken, this results in the intersection of the labels rather than the union.
I think the workaround here is to provide a placement manifest.