Thank you for contacting us. I understand your dilemma and it is not possible to make the category bar hidden at this point in time, at least not without using css to hide it (which is not supported by the support agreement).
There are however a few other thins you could to when you build your site-navigation.
The first thing to look at is to add sub-categories to limit the amount of main categories that you have, and by doing this you can re-structure your spaces and categories.
Manual category permissions
This may be a more convenient way to make the category bar smaller. Without manual category permissions turned on, categories that contain spaces that the user is allowed to see will show up at the site-menu. Turning on manual category permission (learn more here: https://docs.refinedwiki.com/display/rwot/Categories#Categories-ManualCategoryPermissions), you can decide what categories are shown to what users. Users will still be able to see the spaces, but not any category dashboards that you may have setup.
Let me know if you have any further questions!
Best Regards, Maria Heij
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