It took a while, if you're looking for a solution it's here:
Example for [Category Manager]
Nominally it is: Category Parent Id [cat_parent_id] in TYPE: Category
In its place, a new Field in TYPE: Select / Dynamic
When creating a new type:
Label: ???
Query: Construction
Select Label: Select
Table: #__categories
Optional Name: title
Where: published = 1 AND path LIKE "%NAME OF CATEGORY/SUBCATEGORY%"
Options Value: id
SAVE/CLOSE
Search Form - Fields
1: Filter
3:Nested Exact+ (tick #__categories tables)
It works: maybe there are other ways.
I don't know how to make dashes/characters
[main category]
--[sub category-1]
---[sub category-2]
You cannot distinguish in the drop-down list which is the main category.