To do Alt + P T H B on Mac in Excel, download and install Accelerator Keys, then press Option, followed by P, T, H, and B.
Command: Browse Themes
This is how to do Alt + P T H B 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 + P T H B opens a file browser to locate and apply custom theme files (.thmx) from your computer. This allows you to use themes you’ve downloaded or created, or themes shared by colleagues to maintain brand consistency.