If you assign two report categories with different access to a role or a user, these access rights still exist individually for each category and are not used globally.
You assign two different roles to user A, each of which is assigned a report category.
For category A (management-reports), role A only has access to view the reports. The role cannot create, share, edit, or delete reports. Role B has access rights to category B (marketing-reports) and can view, create, share, edit, and delete the reports in this category.
If now both roles are added for user A, he also has exactly these rights. The access rights apply per category and are not transferred to the user in their entirety. Although the user has the right to create reports in category B, this is still not possible in category A.
In our example, the user can edit marketing-reports, but not management-reports.