Background property is not applied on Android and WinUI. On Mac and iOS works as expected.
<telerik:RadButton x:Name="button" Text="hello telerik button">
<telerik:RadButton.Background>
<LinearGradientBrush EndPoint="0,1">
<GradientStop Offset="0.0" Color="Violet" />
<GradientStop Offset="1.0" Color="DarkRed" />
</LinearGradientBrush>
</telerik:RadButton.Background>
</telerik:RadButton>