ToggleButtuons ItemsControl only one will be Checked at a time

I have this ItemsControl that every item is ToggleButton.

public List<string> MyList { get; set; } = new() {"A", "B", "C", "D"};

<ItemsControl ItemsSource="{Binding MyList}">
    <ItemsControl.ItemTemplate>
        <DataTemplate>
            <ToggleButton Content="{Binding}"/>
        </DataTemplate>
    </ItemsControl.ItemTemplate>
</ItemsControl>

How is it possible that only one item will be checked at a time?

I want to avoid this situation

Instead of an ItemsControl, you may use a ListBox with a ListBoxItem Style that declares the ToggleButton in its ControlTemplate.

Bind the IsChecked property of the ToggleButton to the IsSelected property of the ListBoxItem. The default SelectionMode of a ListBox is Single, so only one item will ever be selected and hence checked.

Be aware that you can not use a TemplateBinding because it is inherently one-way.

<ListBox ItemsSource="{Binding MyList}">
    <ListBox.ItemContainerStyle>
        <Style TargetType="ListBoxItem">
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="ListBoxItem">
                        <ToggleButton
                            Content="{Binding}"
                            IsChecked="{Binding IsSelected,
                                RelativeSource={RelativeSource TemplatedParent}}"/>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>
    </ListBox.ItemContainerStyle>
</ListBox>

An alternative may be RadioButtons that share a GroupName. You would have to style them to look like ToggleButtons.

<ItemsControl ItemsSource="{Binding MyList}">
    <ItemsControl.ItemTemplate>
        <DataTemplate>
            <RadioButton
                Style="{StaticResource ResourceKey={x:Type ToggleButton}}"
                Content="{Binding}"
                GroupName="Buttons"/>
        </DataTemplate>
    </ItemsControl.ItemTemplate>
</ItemsControl>