When the control is added inside Grid star-sized Row, or directly to the page, the control does not fill into the page height and width. The behavior occurs only when project targets .NET 7
Use this code:
<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
xmlns:telerik="http://schemas.telerik.com/2022/xaml/maui"
x:Class="MauiApp2.MainPage">
<telerik:RadSideDrawer x:Name="drawer"
DrawerLength="200">
<telerik:RadSideDrawer.MainContent>
<Grid BackgroundColor="LightBlue">
<Label Text="Main content" />
</Grid>
</telerik:RadSideDrawer.MainContent>
<telerik:RadSideDrawer.DrawerContent>
<VerticalStackLayout Spacing="10" BackgroundColor="LightCoral"
Padding="10, 10, 0, 0">
<Button Text="Mail"/>
<Button Text="Calendar" />
<Button Text="People" />
<Button Text="Tasks" />
</VerticalStackLayout>
</telerik:RadSideDrawer.DrawerContent>
</telerik:RadSideDrawer>
</ContentPage>
This is the result on Android: