也许像这样。

public class MyDatePicker : DatePicker
{
    private string _format = null;
    public static readonly BindableProperty NullableDateProperty = BindableProperty.Create<MyDatePicker, DateTime?>(p => p.NullableDate, null);
    public DateTime? NullableDate
    {
        get { return (DateTime?)GetValue(NullableDateProperty); }
        set { SetValue(NullableDateProperty, value); UpdateDate(); }
    }
    private void UpdateDate()
    {
        if (NullableDate.HasValue) { if (null != _format) Format = _format; Date = NullableDate.Value; }
        else { _format = Format; Format = "pick ..."; }
    }
    protected override void OnBindingContextChanged()
    {
        base.OnBindingContextChanged();
        UpdateDate();
    }
    protected override void OnPropertyChanged(string propertyName = null)
    {
        base.OnPropertyChanged(propertyName);
        if (propertyName == "Date") NullableDate = Date;
    }
}

在Xaml中

<local:MyDatePicker x:Name="myDatePicker"></local:MyDatePicker>

在主页. cs中

{
        InitializeComponent();
        myDatePicker.NullableDate = null;
    }

在Maui，DatePicker字段可以为空，这是一个需要增强的功能，有人在GitHub上提交了申请，你可以关注一下：[Enhancement] DatePicker and TimePicker should support DateOnly? and TimeOnly?