Customize → Category
This is category page eg :Category Demo in here you can setting layout of this page
So when you in the Customize then you should click to Category
Then click to the Blogs Categories.
Sidebar Layout
Right Sidebar.
You can read more for the widgets at here : Sidebar
Post Layout
You can setting layout posts for yourself
List Post.
Grid Post.
or you can use post layout with sidebar layout e.g
And some customizations for post layout
