While editing a template, you can also choose its default category or subcategory.
First, navigate to the template editor.
Step 1. In the template editor, click Choose Category / Subcategory in the upper left corner.
Step 2. In the pop-up that will appear, choose the category and subcategory of the template. Once done, click Move draft.
Now, when a new page is created from that template, it will automatically be categorized in the default category.