In Mojave and Catalina you can make a video recording of the entire screen or just a selected portion of it using the built in Screenshot feature without using QuickTime. Press Command-Shift-5 and a control bar will appear at the bottom of your screen. To record the entire screen, click on the button that shows a screen with a solid outline and a circle in the corner. If you would like to record a specific portion of your screen, click the button that shows a screen with a dotted outline with a circle in the corner. A highlighted area will appear that you can rearrange with your mouse. When you're ready, click Record on the control bar. To stop recording, click the stop button in the menu bar at the top of your screen or press Command-Control-Esc.