private void ApplyScale(double delta)
{
    var resources = Application.Current.Resources;
    // Adjust size
    AdjustFontSize(resources, "FontSize.M",  delta);

    this.Dispatcher.InvokeAsync(() =>
    {
        foreach (var tb in this.ChildrenOfType<RadWatermarkTextBox>().Where(x => x.IsLabelFloated))
            FixLabelRowHeight(tb);
    }, DispatcherPriority.Loaded);
}

private static void FixLabelRowHeight(RadWatermarkTextBox tb)
{
    var rootGrid = tb.ChildrenOfType<Grid>().FirstOrDefault(g => g.Name == "RootElement");
    if (rootGrid == null) return;

    var labelEl = tb.ChildrenOfType<TelerikLabel>().FirstOrDefault(l => l.Name == "PART_LabelVisualElement");
    if (labelEl == null) return;

    RowDefinition? labelRow = rootGrid.RowDefinitions
        .FirstOrDefault(r => r.Name == "PART_LabelRowDefinition")
        ?? rootGrid.RowDefinitions.ElementAtOrDefault(Grid.GetRow(labelEl));

    if (labelRow == null) return;

    if (labelRow.Height != GridLength.Auto)
    {
        labelRow.Height = GridLength.Auto;
    }
}