To do Alt + h b b on Mac in Excel, download and install Accelerator Keys, then press Option, followed by h, b, and b.
Command: Bottom Double Border
This is how to do Alt + h b b 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 b activates the Bottom Double Border command in Excel, providing quick access to this feature from the ribbon.