In a scenario where you are trying to set the AppointmentsSource of the RadCalendar in the OnAppearing event of the Page, a NullReferenceException is thrown in the Telerik.XamarinForms.InputRenderer.WinRT.CalendarAdapter UpdateAppointmentsSource method. A workaround is to make the OnAppearing method async and await the action that sets the AppointmentSource.
The more appointments you add to the AppointmentsSource, the poorer the performance of the Calendar is. This can be observed when switching months in month view. In case you have a huge amount of appointments, switching the months takes time. The issue is specifically obvious when a single month contains lots of appointments(600 for example). However, it is present when you are switching months that do not have any appointments at all as well.
Currently MonthNames view is available only in iOS
Please expose a collection of Day objects for the currently visible days in the Calendar's view. Potentially in a RadCalendar.VisibleDays property. This would be needed to get the trailing and leading days of the previous and next month. For example, see the attached screenshot.