To do Alt + H B W on Mac in Excel, download and install Accelerator Keys, then press Option, followed by H, B, W.
Command: Draw Border
This is how to do Alt + H B W 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 W draw Border lets you draw borders by clicking and dragging on cell edges. Your cursor becomes a pencil that creates borders where you click.