There are several ways to display categories in your reports, David. If you are referring to categorising a bank transaction, the category you select in the Account section will appear in the Split Account column of the Balance Sheet Detail report.

To address your second concern, yes, it is necessary to categorise each transaction in QuickBooks Online (QBO) to ensure accurate tracking in your reports.
However, if you’re running a sales transaction report, the results will be based on the corresponding income account linked to each product or service. And for an expenses transaction report, the categories reflected will depend on the specific categories assigned to each transaction.
I’d be glad to hear updates from you regarding the specific reports you’d like to generate. If you have any further questions or need assistance, please know that we’re here to help you anytime.