To do Alt + L G on Mac in Excel, download and install Accelerator Keys, then press Option, followed by L, G.
Command: Group Box (Form Control)
This is how to do Alt + L G 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 + L g inserts a Group Box form control. Group boxes visually organize related controls on your worksheet, such as grouping option buttons together so only one can be selected at a time within that group.