To do Alt + 3 on Mac in Excel, download and install Accelerator Keys, then press Option, followed by 3.
Command: Quick Access Position 3 (user-customizable)
This is how to do Alt + 3 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 + 3 activates the third button in your Quick Access Toolbar. By default on Windows, this is typically Undo, but you can customize it to any command you frequently use. The Quick Access Toolbar appears at the top-left of Excel, making these shortcuts some of the fastest ways to access your most-used features.