To do Alt + A G A on Mac in Excel, download and install Accelerator Keys, then press Option, followed by A, G, A.
Command: Auto Outline
This is how to do Alt + A G A 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 + A G A auto Outline automatically creates an outline based on the structure of your data. Excel analyzes formulas and groupings to determine which rows and columns should be grouped together.