To do Alt + h l h l on Mac in Excel, download and install Accelerator Keys, then press Option, followed by h, l, h, l.
Command: Highlight Cells Less Than
This is how to do Alt + h l h l 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 l h l creates a rule to highlight cells with values less than a specified number. You can choose the highlight color.