public partial class MainPage : ContentPage
{
    public ObservableCollection<InvoiceItem> Items { get; } = new()
    {
        new InvoiceItem { Price = 100m },
        new InvoiceItem { Price = 200m },
        new InvoiceItem { Price = 300m },
    };

    public MainPage()
    {
        InitializeComponent();
        BindingContext = this;

        this.dataGrid.Commands.Add(new CustomDataGridEditingCommand());
    }
}

public class InvoiceItem : INotifyPropertyChanged
{
    private const decimal FullTaxRate = 0.19m;
    private const decimal HalfTaxRate = 0.07m;

    private decimal price;
    private decimal prop1;
    private decimal prop2;

    public bool SupressPropertyChanged { get; set; }

    public decimal Price
    {
        get => price;
        set
        {
            if (SetProperty(ref price, value))
            {
                this.UpdateAggregates();
            }
        }
    }

    public decimal Prop1
    {
        get => prop1;
        set => SetProperty(ref prop1, value);
    }

    public decimal Prop2
    {
        get => prop2;
        set => SetProperty(ref prop2, value);
    }

    public event PropertyChangedEventHandler? PropertyChanged;

    protected void RaisePropertyChanged([CallerMemberName] string? propertyName = null)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }

    public void UpdateAggregates()
    {
        if (this.SupressPropertyChanged)
        {
            return;
        }

        Prop2 = price * HalfTaxRate;
        Prop1 = price * FullTaxRate;
    }

    private bool SetProperty<T>(ref T field, T value, [CallerMemberName] string? propertyName = null)
    {
        if (EqualityComparer<T>.Default.Equals(field, value))
        {
            return false;
        }

        field = value;
        RaisePropertyChanged(propertyName);
        return true;
    }
}

public class CustomDataGridEditingCommand : DataGridCommand
{
    public CustomDataGridEditingCommand()
    {
        this.Id = DataGridCommandId.CommitEdit;
    }

    public override void Execute(object parameter)
    {
        if (parameter is EditContext context)
        {
            var item = context.CellInfo.Item as InvoiceItem;

            item.SupressPropertyChanged = true;
            this.Owner.CommandService.ExecuteDefaultCommand(DataGridCommandId.CommitEdit, parameter);
            item.SupressPropertyChanged = false;

            this.Owner.Dispatcher.DispatchDelayed(TimeSpan.FromMilliseconds(10), () => item.UpdateAggregates());
        }
    }
}

    <telerik:RadDataGrid x:Name="dataGrid"
                     ItemsSource="{Binding Items}"
                     AutoGenerateColumns="False"
                     ShowColumnFooters="True">
        <telerik:RadDataGrid.Columns>

            <telerik:DataGridNumericalColumn  PropertyName="Price"
                                         HeaderText="Price">
                <telerik:DataGridNumericalColumn.AggregateDescriptors>
                    <telerik:PropertyAggregateDescriptor PropertyName="Prop1"
                                                         Function="Sum" />
                    <telerik:PropertyAggregateDescriptor PropertyName="Prop2"
                                                         Function="Sum" />
                </telerik:DataGridNumericalColumn.AggregateDescriptors>
            </telerik:DataGridNumericalColumn>
        </telerik:RadDataGrid.Columns>
    </telerik:RadDataGrid>