
Explanation:
Categories are "The categories to search. Categories can be defined by users by using Outlook or Outlook on the web... The possible values are red, blue, green, etc." ItemClass: "Use this property to search specific third-party data types that your organization imported to Office 365." We are not importing any third-party data types.
Kind: "The type of email message to search for. Possible values: contacts, microsoftteams, meetings, etc."
https://learn.microsoft.com/en-us/purview/ediscovery-keyword-queries-and-search-conditions