MainPage.xaml

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:local="clr-namespace:MauiAppImageSourceFromFileBug"
             x:Class="MauiAppImageSourceFromFileBug.MainPage">

    <ContentPage.Resources>
        <local:NullConverter x:Key="MyNullConverter" />
    </ContentPage.Resources>

    <ScrollView>
        <VerticalStackLayout>

            <!-- Selection view: -->
            <CollectionView ItemsSource="{Binding Items}"
                            SelectedItem="{Binding SelectedItem}"
                            SelectionMode="Single"
                            Margin="0">
                <CollectionView.ItemsLayout>
                    <LinearItemsLayout Orientation="Vertical"
                                       ItemSpacing="0" />
                </CollectionView.ItemsLayout>
                <CollectionView.ItemTemplate>
                    <DataTemplate>
                        <VerticalStackLayout Padding="15"
                                             Margin="15">
                            <Label Text="{Binding Name}" />
                        </VerticalStackLayout>
                    </DataTemplate>
                </CollectionView.ItemTemplate>
            </CollectionView>

            <!-- Details view: -->
            <VerticalStackLayout BindingContext="{Binding SelectedItem}">
                <Label Text="SelectedItem:" />
                <Label Text="{Binding Name}" />

                <Image Aspect="AspectFill"
                       Source="{Binding ImageSource}"
                       Margin="0, 20, 0, 20">
                    <Image.Style>
                        <Style TargetType="Image">
                            <Setter Property="IsVisible"
                                    Value="false" />
                            <Style.Triggers>
                                <!-- Workaround, because the ImageSource doesn't update after a null value is set -->
                                <DataTrigger TargetType="Image"
                                             Binding="{Binding ImageSource, Converter={x:StaticResource MyNullConverter}}"
                                             Value="false">
                                    <Setter Property="IsVisible"
                                            Value="true" />
                                </DataTrigger>
                            </Style.Triggers>
                        </Style>
                    </Image.Style>
                </Image>

            </VerticalStackLayout>
        </VerticalStackLayout>

    </ScrollView>

</ContentPage>