If you write anything in Shared Notes section of the 1-on-1, the meeting attendees (manager and direct report) can view those notes. You can write your talking points and action items in these Shared Notes.
These notes are not visible to anyone beyond the meeting attendees - that is the manager and the direct report having their 1-on-1
If you write anything in the Private Notes section that’s below the Shared Notes box, they will only be visible to you. Your private notes are not accessible to the other attendee.