Category security feature: new topics visible to moderators (and up) only

I would like to have a category where new topics are visible to moderators only (or configurable to any user group). The moderator can then decide to publish the topic for all to see.
This might be implemented via the ‘unlisted’ feature. Or it might be done as an extension to the category security options.
Is there any existing workaround that would achieve this?

Use a PM to a group, once approved have mods move PM to a category

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