The width of RadEntry, RadMaskedEntry, and RadComboBox are the same on windows, android and ios. On mac there is difference when the width of the defined Column is set to * in grid: 

MacCatalyst:

Windows:

Whenever the combobox doesn't have enough space to be displayed on the screen, the footer gets pushed to the bottom and off the dropdown popup.

This was tested on Telerik 3.0 but I also tested it on 3.1, 3.2, 3.2.1, and 4.0 with the same results. 

When setting SelectedItem and using static data for the ItemsSource, Layout cycle detected. Layout could not complete exception is thrown
Setup:

<telerik:RadComboBox x:Name="ComboBox" 
                                 SelectedItem="{Binding SelectedItem, Mode=TwoWay}">
                <telerik:RadComboBox.ItemsSource>
                    <x:Array Type="{x:Type x:String}">
                        <x:String>USA</x:String>
                        <x:String>Uganda</x:String>
                        <x:String>Ukraine</x:String>
                        <x:String>Canada</x:String>
                        <x:String>France</x:String>
                        <x:String>Italy</x:String>
                        <x:String>United Kingdom</x:String>
                        <x:String>China</x:String>
                        <x:String>Japan</x:String>
                    </x:Array>
                </telerik:RadComboBox.ItemsSource>
            </telerik:RadComboBox>

Telerik RadComboBox for MAUI looses focus and triggers unfocus event after selecting an item from the dropdown. This behavior works fine on first time page loading. But if we navigate to some other page and then navigate back to the first page then, upon selecting any item from combobox it closes the dropdown but does not loose the focus and hence does not trigger unfocus event.

We are using the unfocus event with event to command behaviour and ultimately triggering a command in viewmodel. This works fine the first time but after navigation it does not work.

It appears that by the amount of problems that I have encountered so far that Telerik UI for .NET MAUI has not been tested at all on IOS.

Your own ControlSamples do not run for IOS.

Anyway..

Next problem.

IOS Specific only.

           <telerik:RadComboBox ItemsSource="{Binding Items}"
                                     Placeholder="Select Status"
                                     IsDropDownClosedOnSelection="True"/>

note that to use the Telerik Custom Controls it is necessary to either add an x:name to each control, or dummy instantiate each one.

This can be done in MauiProgram.cs.

Add line

  _ = new RadComboBox();

A runtime error occurs when using telerik:RadComboBox and the application will abort.

In RadComboBox, when entering text to filter the items in dropdown, it would be nice to have the first item selected by default that matches the filter and also have the ability to select different item by keyboard up/down arrows.

This feature probably does not make sense on mobile platforms, but it would be great on desktop platforms.