For what I understood, you want to create a template that shows header, footer and blog posts in the body of the page. For that, you will have to create a custom template. Custom templates can be used in several ways, but I’m going to use an example that will give you the option to … Read more
A certain theme is forcing it’s singular post layout
Give custom page template a custom post ID
Prevent header and footer from loading on specific pages with template or plugin
How to change Elementor Template for Single Page Post on Load
It should be single-gruppen.php, not page-gruppen.php. Try renaming your file. This is the explanation of why that works from the template hierarchy: https://developer.wordpress.org/themes/basics/template-hierarchy/#single-post
Virtual page and loading template
The correct way to create a Blog page in WordPress is to create a page and then in Settings > Reading assign that page as the Posts page. To create or customise the template used by the blog, you need to refer to the Template Hierarchy. You’ll notice that the “Blog Posts index page”, which … Read more
Add custom categories and subcategories and posts as custom pages
How To Display Posts Of Custom Post Type At Page Template