To do Alt + A J on Mac in Excel, download and install Accelerator Keys, then press Option, followed by A, J.
Command: Show Detail
This is how to do Alt + A J 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 J expands a collapsed group to show its detail rows or columns. When you have grouped and hidden data in an outline, this command reveals the underlying detail for the selected summary row or column.