Just move anywhere to clear the highlight. The Extend Selection mode turns off as soon as you do an action.
Sometimes this approach creates problems such as the runaway mouse where we lose exact control over the amount of text we want to select in a Word document. The most common way to select or highlight text is to click and drag your mouse across the text.
Almost every editing and formatting task begins by selecting something, that is, to Select Then Do. We select document text to format, copy, move, and delete. Besides entering text, selecting text is probably the most common task for many Microsoft Word documents.