@Tui17
You can only view notes on past dates if you turn on Professional Hosting Tools and use the multicalendar to view the notes. Hover over the date to see the note. You can only use the multicalendar on the desktop - not the App.
Airbnb removed the ability to add a note to blocked or open dates after the recent release. You can add/edit notes using the multicalendar (only a desktop not the App). You can still add notes on the regular calendar to a reservation.
Yesterday, I noticed you can add a note now to a blocked date on the regular calendar (but not for open dates). You will have to continue to use the multicalendar for adding notes to open dates on the calendar.
