“In custom fields, is it possible to create multi-choice subcategories? For example, if I select ‘A’ in the first custom field, the second field shows a list of fruits. If I select ‘B’ in the first field, it shows a list of animals. Or is there another way to do this?”
SeeCategories are based on in the dependent (“child”) CF’s Basics panel. Select the source (“parent”) CF in the dependent’s pulldown. Then create the mapping in the Values area, which will have an extra Category field.