Profile: martinP-13

Problem:
Can a Content Template only be assigned to posts and replace their Post Body or can we also use this elsehow?

Solution:
Content Templates, if assigned to a post, will replace the Content of that post.
If you need to display a Content Template independently from the Post Body you'd need to use PHP or other methods to output it in the Themes sections you want which are not the post body.

[wpv-post-body view_template="slug-of-your-content-template"]

is a shortcode, and classically in WordPress you will insert this in a Text Editor of a Post, or else, you can hence display this anywhere you have Text Editors and output that content somehow in the Front End.

You can also insert a Content Template ShortCode in PHP Templates using do_shortcode(), but better would be to use Views API to display that Content Template in PHP:
https://toolset.com/documentation/programmer-reference/views-api/#render_view_template