To do Alt + N J on Mac in Excel, download and install Accelerator Keys, then press Option, followed by N and J.
Command: Object
This is how to do Alt + N J 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 J opens the Object dialog to embed or link external files into your spreadsheet. You can insert documents, PDFs, other Office files, or create new embedded objects that can be edited in place.