Absolutely eliminate "Automatic new Desktop when dragging"
Not seeing this behavior. I have several desktops enabled, yes macOS will happily slide to the next available if I drag a file/window to the extreme right of the screen, but it won't create NEW desktops. Once I hit #4 (the last desktop I have enabled) holding a file against the right side of the screen doesn't trigger any action. Perhaps you have more than 1 screen enabled in Mission Control? Remove them, it should not auto-create more. (added as answer per request!)