Hi Samir,
Thank you for contacting Syncfusion support.
Your requirement of customizing Calendar MonthView in Xamarin.Forms can be achieved by setting Custom view to the month cell using OnMonthCellLoadedEvent or setting CellTemplate of Calendar MonthViewSettings. Based on your requirement, you can customize the calendar UI elements, using the same.
You can customize the Header as well,
We have Customization sample in our Calendar Sample browser sample and it is in MVVM pattern. you can download and refer the same by the following GitHub link.
We hope this helps. Please let us know, if you would require any further assistance.
Regards,
Subburaj Pandian V