To do Alt + N S C on Mac in Excel, download and install Accelerator Keys, then press Option, followed by N, S, and C.
Command: Screenshot Menu
This is how to do Alt + N S C 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 + N S C opens the Screenshot menu showing thumbnails of available windows to capture, plus the Screen Clipping option. Quickly insert screenshots of other applications directly into your spreadsheet without leaving Excel.