Wouldn’t it be cool if you could enable pause in QuickTime for macOS? Well, you can (before Catalina) and here is a demonstration.
Once your recording starts, QuickTime for macOS may hide itself leaving only the stop button on the menu and its icon on the dock. You will want to click on the QuickTime for macOS icon on the dock and that will make it the focus on the menu when you can now click on the ‘Esc’ key on your keyboard to bring up the Screen Recording window. The Screen Recording will give you the option to pause when you press and hold the ‘Alt’ key on the keyboard.