DiffableDataSourceExtensions.cs

public static class DiffableDataSourceExtensions
{
    public static NSDiffableDataSourceSnapshot<IdentifierType<TSection>, IdentifierType<TItem>>
        ToDiffableDataSourceSnapshot<TSection, TSectionIdentifier, TItem, TItemIdentifier>(
            this IEnumerable<TSection> sections, Func<TSection, TSectionIdentifier> getSectionIdentifier,
            Func<TSection, IEnumerable<TItem>> getItems, Func<TItem, TItemIdentifier> getItemIdentifier)
    {
        var snapshot = new NSDiffableDataSourceSnapshot<IdentifierType<TSection>, IdentifierType<TItem>>();

        foreach (var section in sections)
        {
            var items = getItems(section);

            var sectionIdentifier = IdentifierType.For(section, getSectionIdentifier);
            var itemIdentifiers = items.Select(item => IdentifierType.For(item, getItemIdentifier)).ToArray();

            snapshot.AppendSections(new[] { sectionIdentifier });
            snapshot.AppendItems(itemIdentifiers);
        }

        return snapshot;
    }
}

EasyUITableViewDiffableDataSource.cs

public class EasyUITableViewDiffableDataSource<TSection, TSectionIdentifier, TItem, TItemIdentifier>
        : UITableViewDiffableDataSource<IdentifierType<TSection>, IdentifierType<TItem>>, IUITableViewDiffableDataSource<TSection>
{
    Func<TSection, TSectionIdentifier> _getSectionIdentifier;
    Func<TSection, IEnumerable<TItem>> _getSectionItems;
    Func<TItem, TItemIdentifier> _getItemIdentifier;
    Func<UITableView, int, TSection, string> _titleForHeader;
    Func<UITableView, int, TSection, string> _titleForFooter;

    NSDiffableDataSourceSnapshot<IdentifierType<TSection>, IdentifierType<TItem>> _snapshot;

    public EasyUITableViewDiffableDataSource(
        UITableView tableView,
        Func<TSection, TSectionIdentifier> getSectionIdentifier,
        Func<TSection, IEnumerable<TItem>> getSectionItems,
        Func<TItem, TItemIdentifier> getItemIdentifier,
        UITableViewDiffableDataSourceCellProvider cellProvider,
        Func<UITableView, int, TSection, string> titleForHeader = null,
        Func<UITableView, int, TSection, string> titleForFooter = null
        ) : base(tableView, cellProvider)
    {
        _getSectionIdentifier = getSectionIdentifier;
        _getSectionItems = getSectionItems;
        _getItemIdentifier = getItemIdentifier;
        _titleForHeader = titleForHeader;
        _titleForFooter = titleForFooter;
    }

    public void ApplySnapshot(IEnumerable<TSection> sections, bool animatingDifferences)
    {
        _snapshot = sections.ToDiffableDataSourceSnapshot(
            _getSectionIdentifier, _getSectionItems, _getItemIdentifier);

        ApplySnapshot(_snapshot, animatingDifferences);
    }

    public override string TitleForHeader(UITableView tableView, nint section)
        => _titleForHeader?.Invoke(tableView, (int)section, _snapshot.SectionIdentifiers[section].Item);

    public override string TitleForFooter(UITableView tableView, nint section)
        => _titleForFooter?.Invoke(tableView, (int)section, _snapshot.SectionIdentifiers[section].Item);
}

EasyUITableViewDiffableDataSourceHelper.cs

public static class EasyUITableViewDiffableDataSource
{
    public static IUITableViewDiffableDataSource<TSection> Create<TSection, TSectionIdentifier, TItem, TItemIdentifier>(
        UITableView tableView,
        List<TSection> items,
        Func<TSection, TSectionIdentifier> getSectionIdentifier,
        Func<TSection, IEnumerable<TItem>> getSectionItems,
        Func<TItem, TItemIdentifier> getItemIdentifier,
        Func<UITableView, NSIndexPath, TItem, UITableViewCell> getCell,
        Func<UITableView, int, TSection, string> titleForHeader = null,
        Func<UITableView, int, TSection, string> titleForFooter = null)
        => new EasyUITableViewDiffableDataSource<TSection, TSectionIdentifier, TItem, TItemIdentifier>
        (
            tableView, getSectionIdentifier, getSectionItems, getItemIdentifier,
            (tv, indexPath, item) => getCell(tv, indexPath, (item as IdentifierType<TItem>).Item),
            titleForHeader, titleForFooter
        );
}

FuncIdentifierType.cs

public class FuncIdentifierType<T,U> : IdentifierType<T>
{
    private readonly Func<T, U> _identifierFunc;

    public FuncIdentifierType(T item, Func<T,U> identifierFunc) : base(item)
    {
        _identifierFunc = identifierFunc;
    }

    // invoke the provided func and hash the result
    public override nuint GetNativeHash()
        => (nuint)_identifierFunc(Item).GetHashCode();

    public override bool IsEqual(NSObject anObject)
        => GetNativeHash() == anObject.GetNativeHash();
}

IdentifierType.cs

public static class IdentifierType
{
    public static IdentifierType<T> For<T>(T item) => new IdentifierType<T>(item);
        
    public static IdentifierType<T> For<T,U>(T item, Func<T, U> getIdentifier) => new FuncIdentifierType<T,U>(item, getIdentifier);
}
    
public class IdentifierType<T> : NSObject
{
    public readonly T Item;

    public IdentifierType(T item)
    {
        Item = item;
    }

    // pass-through the .NET hash
    public override nuint GetNativeHash()
        => (nuint) Item.GetHashCode();

    public override bool IsEqual(NSObject anObject)
        => GetNativeHash() == anObject.GetNativeHash();
}

InterfaceIdentifierType.cs

public interface IIdentifier
{
    string Identifier { get; }
}

public class IIdentifierType<T> : IdentifierType<T>
        where T: IIdentifier
{
    public IIdentifierType(T item) : base(item) {}

    // read the identifier and take its hash
    public override nuint GetNativeHash()
        => (System.nuint)Item.Identifier.GetHashCode();

    public override bool IsEqual(NSObject anObject)
        => GetNativeHash() == anObject.GetNativeHash();
}

IUITableViewDiffableDataSource.cs

public interface IUITableViewDiffableDataSource<TSection>
{
    void ApplySnapshot(IEnumerable<TSection> sections, bool animatingDifferences);
}

NSDiffableDataSourceSnapshotHelper.cs

public static NSDiffableDataSourceSnapshot<IdentifierType<TSection>, IdentifierType<TItem>>
    ToDiffableDataSourceSnapshot<TSection, TSectionIdentifier, TItem, TItemIdentifier>(
        this IEnumerable<TSection> sections, Func<TSection, TSectionIdentifier> getSectionIdentifier,
        Func<TSection, IEnumerable<TItem>> getItems, Func<TItem, TItemIdentifier> getItemIdentifier)
{
    var snapshot = new NSDiffableDataSourceSnapshot<IdentifierType<TSection>, IdentifierType<TItem>>();

    foreach (var section in sections)
    {
        var items = getItems(section);

        var sectionIdentifier = IdentifierType.For(section, getSectionIdentifier);
        var itemIdentifiers = items.Select(item => IdentifierType.For(item, getItemIdentifier)).ToArray();

        snapshot.AppendSections(new[] { sectionIdentifier });
        snapshot.AppendItems(itemIdentifiers);
    }

    return snapshot;
}

PassthroughIdentifierType.cs

public class IdentifierType<T> : NSObject
{
    public readonly T Item;

    public IdentifierType(T item)
    {
        Item = item;
    }

    // pass-through the .NET hash
    public override nuint GetNativeHash()
      => (nuint) Item.GetHashCode();

    public override bool IsEqual(NSObject anObject)
      => GetNativeHash() == anObject.GetNativeHash();
}

Using EasyUITableViewDiffableDataSourceHelper.cs

var source =
  EasyUITableViewDiffableDataSource.Create(
    TableView,                                                      
    items: Games,                                                   // used for type inference, can be null at the time of the call
    getSectionIdentifier: game => game.GameName,                    // return key for section
    getSectionItems:      game => game.Characters,                  // return items for section
    getItemIdentifier:    character => character.CharacterName,     // return key for item
    getCell: (tv, indexPath, character) =>                          // standard GetCell, but includes typed model parameter (character)
    {
        // yeah yeah cell reuse
        var cell = new UITableViewCell(UITableViewCellStyle.Default, "cell");
        cell.TextLabel.Text = character.CharacterName;

        return cell;
    },
    titleForHeader: (tv, sectionIndex, section) => section.GameName);

It will be great. Thank you !

@am-kh I added a small ios sample and quick video if it helps. The main issue at the moment is the 'register attribute' hack; since I am doing some Microsoft.iOS work soon I will improve this aspect. I improved that and updated the sample.