You can create up to two additional levels of subcategories and sub-subcategories.
Customize the categories to your needs:
What to do if you cannot create a subcategory?
For existing categories with assigned transactions, subcategories can NOT be created, because a parent category represents the sum of its subcategories.
Simply create a new category instead, which will then serve as the parent category.
If existing categories are to be assigned to a new group, a subcategory must first be created in this new category for technical reasons. It can then be deleted again.