featured image automatically assigned from a PODS image field

I created a website where any user can create custom PODS posts with images that are inserted into custom fields. I need these custom posts to have a featured image. The problem is that if I allow the user to choose the feature image (setting on “upload file” in user role) wordpress makes the media library accessible and the user can make disasters. The ideal is that the first or one of the images stored in the custom fields becomes a featured image automatically, without a choose. Or secondly allow the user to choose the featured image but prevent them from accessing the media library, but that doesn’t seem to be possible. Can anyone help me?

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