To do Alt + H B Y on Mac in Excel, download and install Accelerator Keys, then press Option, followed by H, B, Y.
Command: Line Style
This is how to do Alt + H B Y 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 Y line Style opens options to choose the style for borders you draw. You can select from solid, dashed, dotted, Double line styles.