Data categories and visibility are features that allow you to organize and control access to your Salesforce Knowledge articles based on different topics or criteria. Data categories are logical groupings of articles that reflect your business needs and processes. You can create a data category group and assign it to one or more article types, and then create data categories and subcategories within that group. Data category visibility is a setting that determines which data categories users can access based on their profiles or permission sets. You can use data categories and visibility to provide relevant and appropriate product documentation to your customers and support team. References:
https://help.salesforce.com/s/articleView?id=sf.knowledge_categories.htm&type=5
https://help.salesforce.com/s/articleView?id=sf.knowledge_category_visibility.htm&type=5