To do Alt + H + 3 on Mac in PowerPoint, download and install Accelerator Keys, then press Option, followed by H, then 3.
Command: Underline
This is how to do Alt + H + 3 on Mac in PowerPoint with Accelerator Keys, the native ribbon and alt key shortcut solution for Mac users who get more done with PowerPoint.
Alt + H + 3 toggles underline formatting on the selected text. Underlined text has a line beneath it, useful for emphasizing important terms or creating visual hierarchy in your slides.