To do Alt + h l h m on Mac in Excel, download and install Accelerator Keys, then press Option, followed by h, l, h, m.
Command: Highlight Cells More Rules
This is how to do Alt + h l h m 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 m opens the New Formatting Rule dialog where you can create custom highlight rules with more options.