To do Alt + H F K on Mac in Excel, download and install Accelerator Keys, then press Option, followed by H, F, K.
Command: Decrease Font Size
This is how to do Alt + H F K 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 F K decrease Font Size makes the text in selected cells smaller. Each click decreases the size to the next standard font size.