To do Alt + H B on Mac in Excel, download and install Accelerator Keys, then press Option, followed by H and B.
Command: Borders Menu
This is how to do Alt + H 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 opens the Borders dropdown menu in the Font group on the Home tab. From this menu, you can quickly apply various border styles to selected cells including bottom, top, left, right, all borders, outside borders, thick borders, and more. You can also access drawing tools for custom borders and the Format Cells dialog for advanced border options.