How do I correctly set strictly only one desktop?

With Desktops, you can have more than one Desktop.

I want to assign absolutely only one Desktop, not two.

How do I do this exactly?

When I click F3, it looks like this:

(Does that mean I have only one?)

Resolved!

Buscar웃 has identified the issue. I manually deleted the 400 desktops and now this issue:

Absolutely eliminate "Automatic new Desktop when dragging"

is finally resolved.

Solution 1:

That is amazing.

You have created so many desktops that macOS can only display them as a dot.

That line of dots represents your desktops. I did not count but it must be more than 50.

How to delete them.

Press F3

Hold Option Key and keep clicking on the X showing to delete them.

Solution 2:

To your second separate question

Why do I have hundreds of Desktops

Open System preference > Mission Control.

Un-check the Displays have separate Spaces.

That should stop it creating new Desktops.