To do Alt + H O L on Mac in Excel, download and install Accelerator Keys, then press Option, followed by H, O, and L.
Command: Lock Cell
This is how to do Alt + H O 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 O L toggles the Locked property for selected cells. Locked cells cannot be edited when sheet protection is enabled. Use this to control which cells users can modify in a protected worksheet - unlock cells you want editable, keep others locked.