So your question is very, very briefly described. Why don't you just take a screenshot and attach it to your post so that people can see what you want?
Looking into the crystal ball:
I assume you mean the line spacing when you click enter in a Joomla post? That depends on the settings in your Joomla editor, what it does when you click the "enter" (paragraph) key.
Try pressing the Shift key at the same time as the Enter key and see if that doesn't create a gap

Sorry I thought I was clear enough, my apologies.

I don't mean a real enter (where you have placed the arrow) but in your example image I mean the space between the text.
I want the text closer together (less white space between the lines of the text). This is not only for articles, but for everything on the site.

Ok I understand.
I don't know if there is another possibility in your template and maybe it is cleaner, but theoretically you can do the following in your custom CSS (Joomla Backend-> System-> Site Template Styles-> YOUR Template styles -> Column: "CUSTOM CSS" ) enter:

body {

   line height: 1.4rem;

}

The "1.4" regulates the distance. (original 1.8.)
But be careful: This spacing is changed on the entire page. Please keep in mind that you do this at your own risk and there are also mobile devices where this distance may be better for reading the content on small devices.

Sorry for the late response, due to personal circumstances I couldn't respond sooner.
It just had to be line-height instead of line height.

That's how it works fine for me, many thanks!