MiniFrontpage not showing articles from sub categories

I'm using Joomla 3.9.20
This is my categories

Cat-1 (0 article)
. |_ Sub-cat-1 (2 Active )
. |_ Sub-cat-2 (3 Active )
. |_ Sub-cat-3 (1 Active )
Cat-2 (0 article)
. |_ Sub-cat-4 (1 Active )
. |_ Sub-cat-5 (1 Active )
. |_ Sub-cat-6(1 Active )

I want to select Cat-1, and display articles from Sub-cat-1, Sub-cat-2, Sub-cat-3 and ordered by modified date. But it's not showing anything unless I select each subcategory individually.

Is it possible to achieve what I described above? ie. select Cat-1 and show articles from sub-category of Cat-1 (6 articles)

Thanks, in advance.

Mark