Unable to do a partial screen recording on OSX with quicktime

Solution 1:

You can record a selected area of your screen as follows:

• Open the Quicktime Player app
• Choose File -> New Screen Recording or CtrlCommandN
• Now select the area you want to record
• Press the button in the middle of you selected area that states: Start recording
• To stop, there will be a squared stop button that appears in the menu bar

As your screenshot is missing this button, you might want te restart Quicktime Player or reboot your machine.

Solution 2:

As soon as you drag the square, a button should appear in the centre of that area.
Click to Start.

To Stop, there will be a button that appears in the menu bar