A number of RadDataGrid properties can be successfully set in App.xaml, but setting others causes the control to display nothing -- at least in Android.
While I have not tested all possible settings, these results were found experimentally:
Can be used: BackgroundColor, DataOperationIndicatorMode, GridLinesThickness, HorizontalOptions, LoadOnDemandMode, Margin, MinimumHeightRequest, SelectionMode, UserSortMode, VerticalOptions, and ViewportBufferHeight.
Cannot be used in App.Xaml style: AutoGenerateColumns, GridLinesColor, GridLinesVisibility, LoadOnDemandBufferItemsCount, RowHeight, and SelectionUnit.