Important Note after KlintWeb comment:
You certainly want to do any such changes inside a template override.
Search in this site and also in the web about Joomla Template
Overrides to find out how you can create them.
How to wrap the intro-text inside a link to the article:
In components/com_content/views/category/tmpl/blog_item.php there is a ...
Welcome to Stack Exchange.
This is controlled in the menu item. You need to:
Go into your administration section of Joomla!
Click on Menus
Go to the menu that you are using e.g. "main menu"
Select the menu item e.g. "day trips"
Click on the tab called "category"
You can choose the dropdown I show in my image "subcategory levels", set this to "none" and ...
The menu item options are configured using xml files in the front-end views of your components.
Could you compare the configuration file for the "Category Blog" view with one from a working website?
It should have a useglobal="true" parameter for all the fields that have the "Use Global" option.
Joomla does not handle routing well if a single category is assigned to multiple menu items.
The routing system looks for the menu item that the category is assigned to. Once it finds it, it does not look for another one.
This means that if you have a single category assigned to multiple menu items, the routing system (which is responsible for building ...