In the previous versions of Microsoft Word, the Insert button on the keyboard switched between the Insert and Overtype modes. Newer Word versions don't offer this functionality; the Overtype mode is disabled in Word 2016 and Word for Microsoft 365 and newer. To enable the Overtype mode in Word for Microsoft 365 and later, do the following:
In Word for Microsoft 365 equation many symbols can be inserted using a \+name of the symbol: