I’ve created a DateTimePicker class with a bindable property DateTimeValue:

public class DateTimePicker : Grid
{
    private readonly DatePicker datePicker;
    private readonly TimePicker timePicker;
    
    public static readonly BindableProperty DateTimeValueProperty = BindableProperty.Create(nameof(DateTimeValue), typeof(DateTime), typeof(DateTimePicker), defaultBindingMode: BindingMode.TwoWay, defaultValue: DateTime.Today);

    public DateTime DateTimeValue
    {
        set
        {
            SetValue(DateTimeValueProperty, value);
            datePicker.Date = value.Date;
            timePicker.Time = value.TimeOfDay;
        }
        get => (DateTime)GetValue(DateTimeValueProperty);
    }
    ...
}

I pass to a contentPage an instance of this class:

public class ActionDescriptor
{
    public string Note { get; set; }
    public DateTime Moment_1 { get; set; }
}

In this contentPage, I set then BindingContext in the constructor:

BindingContext = action;

action is of type ActionDescriptor.

In the XAML of this contentPage:

<tc:DateTimePicker DateTimeValue="{Binding Moment_1, Mode=TwoWay}" />
<Entry Text="{Binding Note, Mode=TwoWay}" />

The binding on the Entry works fine. The binding on the DateTimePicker does not work.