Problem about add notes.

Hello everyone!

I have found through other posts that Shift + 8 and Alt + 8 can be used to add notes one octave above or below an existing note.
I find with my Mac that Option + 8 adds a note one octave above an existing note, but Shift + 8 does not result in any changes to the existing note.
Could someone please list the recommended Mac keyboard combinations for adding a note one octave above and one octave below an existing note?

Thank you.