In your meeting view, you can see all the events in your calendar, but no one else will be able to see your entire calendar. They will only be able to see the events that they are also invited to.
To clarify, for a 1-on-1 only the manager and the direct report will be able to see those notes. In a meeting, only the meeting attendees will have access to the notes. But if you would like to share the meeting notes, you can use the 'Send Notes' feature and share them with the attendees who attended the meetings and those who did not. (But for a 1-on-1, check with the other person first 😀)
In your personal section, the notes that you write there are only visible to you.
Here is an illustration which may help show what I mean:
If you have invited a third party/external attendee, they will not be able to access the notes within Fellow. (If they click the link "This meeting has notes in Fellow", they will just be brought to a Fellow log-in page). But, if you would like the third party to see the notes or agenda, you can use the Send Agenda/Notes button and send via Slack or email. But they will not be able to edit the notes.