Extending a class while overwriting its properties

public class DiscordEvent : CalendarItem
{
    [Key]
    public int EventId { get; set; }
    public string? Name { get; set; }
    public string? Description { get; set; }
    public DateTime StartDate { get; set; }
    public TimeSpan Duration { get; set; } = TimeSpan.FromHours(1);

    public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
    public DateTime ModifiedAt { get; set; } = DateTime.UtcNow;

    [NotMapped]
    public new string Id { get; set; } = Guid.NewGuid().ToString();
    [NotMapped]
    public new DateTime Start
    {
        get
        {
            return StartDate;
        }
        set
        {
            StartDate = value;
        }
    }
    [NotMapped]
    public new DateTime? End
    {
        get
        {
            return StartDate + Duration;
        }
        set
        {
            value ??= StartDate + Duration;
            Duration = value.Value - StartDate;
        }
    }
    [NotMapped]
    public new bool AllDay { get; set; }
    [NotMapped]
    public new string Text
    {
        get
        {
            return Name ?? string.Empty;
        }
        set { Name = value; }
    }
    [NotMapped]
    public new bool IsMultiDay { get; set; }
}