When collapsing all groups, the footer still keeps bottom position and does not align with the groups. 

In RadListView, the footer is aligned to the groups when they are collapsed. Please provide such option for the CollectionView. 

Provide a built it way to notify the parent group when the items in the nested groups are changed. 

For example, there is no PropertyChanged or CollectionChanged notification that we can hook in to in order to detect updates in parent group headers when the count changes in a subgroup. Only the leaf group headers get updated, but not the parents.

Provide support for right-to-left flow direction: 

The current behavior is that the items

when the device language is set to an RTL language (like Hebrew or Arabic) causing the FlowDirection to be set to RightToLeft, where UI will show correctly with RTL FlowDirection, but the item's corresponding tap areas are still in the LTR positions. 

Having a RadExpander inside the ItemTemplate breaks the Drag and Drop gesture of the RadCollectionView. 

When Using MAUI CollectionView and RadExpander in the template, drag and drop works.

The ItemsSource of the views is populated in the ViewModel of the page. This is done in a command that is triggered by the NavigatedTo event of the page, which is forwarded via EventToCommandBehavior from the Maui Toolkit.

When using the RadCollectionView the loaded items are no longer displayed. 

When the ObservableCollection of the items is completely reconstructed and reassigned the display works.

In the current CollectionView implementation, the CollectionView will start with all the groups expanded. The only way to have any form of preference is to programmatically interact with the DataView after-the-fact https://docs.telerik.com/devtools/maui/controls/collectionview/grouping/expand-collapse

See simple example baaaaif/CollectionViewFilterIssue (MainPage.xaml.cs) to reproduce, click hide and show

When items are filtered through a FilterDescriptor they are hidden - correct
Trying to show the previously hidden items they don't appear again as expected - bug

I've used a BooleanFilterDescriptor and a DelegateFilterDescriptor, both don't work.

Stops me from using the RadCollectionView control

Currently, the LoadOnDemandCollection accepts a callback of the following format in the constructor:

public LoadOnDemandCollection(Func<CancellationToken, IEnumerable> action)

It is a very common scenario to populate the items asynchronously. In its current form the collection would require blocking the current thread to populate the results:

ItemsSource = new LoadOnDemandCollection((cancelationToken) =>
{
    var result = new List<ItemsModel>();
    try
    {
        var items = dataService.GetItemsAsync().Result;

        // TODO: Handle the result.

        return result;
    }
    catch (Exception e)
    {
        // TODO: Handle the exception.
        return null;
    }
});

This is not desired, as using Task.Result blocks the current thread and is considered an anti-pattern, in general.

A better approach would be to add a second overload of the constructor, allowing asynchronous calls:

public LoadOnDemandCollection(Func<CancellationToken, Task<IEnumerable>> action)

This way we can use async and await in the callback instead:

ItemsSource = new LoadOnDemandCollection(async (cancelationToken) =>
{
    var result = new List<ItemsModel>();
    try
    {
        var items = await dataService.GetItemsAsync();

        // TODO: Handle the result.

        return result;
    }
    catch (Exception e)
    {
        // TODO: Handle the exception.
        return null;
    }
});

According to my tests, the first blocking approach is not a problem, as the LoadOnDemandCollection starts a thread internally. That behavior is not obvious however, and using Task.Result is somewhat counterintuitive, so the second approach is much better from the user's perspective.

we have additional field in City class (CountryFlag as Image)

public class City
{
public string Name { get; set; }
public string Country { get; set; }
public Image CountryFlag { get; set; }
}

We want to display the image instead of the property we group by. Provide such option to define which proeprty to be displayed in the group header.