Since the 2023 Summer Release, Calendar Notes are no longer visible/accessible after a date has past on the actual calendar. However, I discovered (by accident) if there was an Airbnb reservation that had a note applied, the notes are still visible on the reservation details as its retained with the reservation information. Scroll to the bottom of reservation details/Calendar Note. If there is a reservation from another synced booking site with a note, it doesn't appear, since it is not attached to an Airbnb reservation.
Might help some Hosts who need to go back and review previous notes that they can't view on the calendar any more.