To hide all category suggestions from the autocomplete section, you can set the number to 0 to disable the Categories sections. Navigate to Stores > Algolia Search > Autocomplete Menu
Alternatively, if you want categories to remain indexed (for analytics or internal usage) but not show up to users, you can add a filter to your front end queries and exclude specific categories. For example, you can add a filter to your search widget by following this guide for customizing your instantSearch results page. You can do this using an event such as beforeWidgetInitialization to add filters / facetFilters using the configure widget.
Lastly, you can prevent your categories from being indexed altogether. If you choose to not index them, you can either choose to not index the products that belong in those categories completely or, you can deactivate the category by navigating to Catalog>Categories and set Include in Menu to No :
In this scenario. you need make sure that the setting Show categories that are not included in the navigation menu is also set to No by navigating to Stores > Algolia Search > Categories.