Wouldn’t it be cool if you could enable pause in QuickTime for macOS? Well, you can (before Catalina) and here is a demonstration.
macOS Mojave and Earlier
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.
macOS Catalina and Later
Sadly, macOS Catalina removes the option to press and hold the ‘Alt’ key on the keyboard to bring up the pause button so you need to pause between your actions so that you have sufficient lead to use the TRIM feature in post production. Also, copying the QuickTime for macOS app from Mojave or early will not work.
If the host is macOS Mojave or earlier and the guest is macOS Catalina, then record with the host with the client in fullscreen.