Currently it is not possible to change value manually by keyboard. The solution is to set [`Focusable = True` for `PART_TextBox`](https://github.com/flarive/Neumorphism.Avalonia/blob/1f9c42e9517d2279fb55e5f607caee49c684881e/Avalonia.Themes.Neumorphism/Themes/NumericUpDown.xaml#L73) What is your opinion?