To do Alt + H B G on Mac in Excel, download and install Accelerator Keys, then press Option, followed by H, B, G.
Command: Draw Border Grid
This is how to do Alt + H B 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 + H B G draw Border Grid lets you draw a grid of borders by clicking and dragging. This creates borders around and between all cells in the selected area.