Why can't I select the entire page range to hide cells?

[anaismorgan]

I'm trying to hide all the unused columns to the right of my table (using Excel 2020 on a Mac) and I've read guidelines saying to shift-command-R to select ALL unused columns...but when I try to do this, Excel says this command "can't be applied to the selected range."

Help please and thank you! How do I clean up this document

[#2]

@anaismorgan 

On Windows that's - select column and Ctrl+Shift+ArrowRight. Thus on Mac it shall be Command+Shift+ArrowRight