To do Alt + N U on Mac in Excel, download and install Accelerator Keys, then press Option, followed by N and U.
Command: Symbol
This is how to do Alt + N U on Mac in Excel with Accelerator Keys, the native ribbon and alt key shortcut solution for Mac users who get more done with Excel.
Alt + N U opens the Symbol dialog to insert special characters not available on your keyboard. You can insert currency symbols, Greek letters, mathematical operators, arrows, and many other special characters from various fonts and character sets.