Hello,
what you are asking for there isn’t possible with the out of the box features so it would be a customization. Some builders and 3rd party widgets have controls for this kind of thing, but it isn’t built into GeoDirectory for categories.
What is built in to GeoDirectory is to hide or show features based on the price package or the CPT. For each CPT you can have completely different CPT settings, tabs, categories, and packages. For price packages, there is a body class added to archive items and listings, a body class for the package, and that can be used to hide items with CSS, or of course there is the built in option to exlude fields by price package.
I have made a note of your idea to use categories only. It could be that we can add a body class to the details page in future versions for the default category. I have made a note of this and the developers will consider it for a future version.
At this time though, it would require a customization and falls outside of what we can help with in support.