Thank you for contacting Syncfusion support.
Based on the provided information, your requirement of Viewing the Popup control in full screen in Xamarin.Forms can be achieved by setting LayoutOptions to the PopupView. Also, by using the ShowFooter, ShowHeader, ShowCloseButton boolean properties you can handle those popup window UI elements.
Please refer the following code example for the same,
We have prepared sample based on your requirement, please find the same by the following link.
Please let us know, if this helpful.
Subburaj Pandian V