Do you want to use RadialGradientBrush
to achieve the same result like circle's screenshot?
If so, here is two running screen result.
Here is code
<StackLayout>
<Frame BorderColor="LightGray"
HasShadow="True"
CornerRadius="12"
HeightRequest="120"
WidthRequest="120">
<Frame.Background>
<!-- Center defaults to (0.5,0.5)
Radius defaults to (0.5) -->
<RadialGradientBrush>
<GradientStop Color="#FF0000"
Offset="0.1" />
<GradientStop Color="#00FF00"
Offset="1.0" />
</RadialGradientBrush>
</Frame.Background>
</Frame>
<Frame BorderColor="LightGray"
HasShadow="True"
CornerRadius="12"
HeightRequest="120"
WidthRequest="120">
<Frame.Background>
<!-- Center defaults to (0.5,0.5)
Radius defaults to (0.5) -->
<RadialGradientBrush Radius="0.5">
<GradientStop Color="#FF0000"
Offset="0.1"/>
<GradientStop Color="#1b7300"
Offset="1"/>
</RadialGradientBrush>
</Frame.Background>
</Frame>
</StackLayout>