Post Loop and Additional argument for query

Hello,

i’m using for the first time the widget “Post Loop” from your Page Builder and i’m trying to display all post from a single category “Kitchens” (slug: “kitchens”) with a content excerpt (max 300 characters) and featured image.

However nothing except the ALL posts are displayed.
I tried:
category_name=kitchens (slug term)
cat=4 (in table wp_terms, kitchens term has the ID 4)

but nothing works.

Any help would be appreciated.
thx