How to show all posts fully collapsed when I click a category?

Here is my Blog, and as you can see I have the Hello World! post open.

When I click a category on the right, this happens:

As you can see there are two posts but they are both “closed”. I would like to have all posts in the category shown as collapsed, aka the full post is visible.

To further explain, lets say I have made 5 posts. Each post contains a picture of a cat, nothing more. All five posts belong to the category “Cats”.

Now I would like to have is so that when I click the category “Cats”, all five images appear. Is this possible to do somehow? I’ve tried to look for a plugin that does this but haven’t been successful.

Thanks in advance!