In another post that is asking the same question that I ultimately have, the top answer says to conditionally format the cells using the formula ###,###. But when I go into conditional formatting, my only options are changing the Font, Border, and Fill of the text...nothing to do with the actual numbers. Help? Microsoft Excel 2016 Mac
As per your screen shot and other web examples, it appears that Excel 2016 for Mac can only format Font, Border and Fill.
From answers.microsoft.com:
Excel for Mac does not have the interface for number formatting in the Conditional Format dialog. The Mac version does respond correctly to Conditional Formatting generated in Excel for Windows.
Why? We can only guess as to Microsoft's thinking. It seems like a large omission.