DataTable dt.Select($"ColumnName='{ABC}'");

ServicePointManager.SecurityProtocol = (SecurityProtocolType)3072 | (SecurityProtocolType)768 | SecurityProtocolType.Tls;

List< AttachTreaty > modelRider = (from m in List< Tready >
                        where m.GetType().Equals(typeof(AttachTreaty))
                        select (AttachTreaty)m).ToList();

usercombo = dbRepository.tbUserComboMain.Where(x => x.Prop_AgentID == AgentID).OrderByDescending(x => x.ModifyDate).
    Select(x => new PropModel()
    {
        propId = x.Prop_ID,
        propNo = x.Prop_Name,
        propType = "C",
        dateTime = x.ModifyDate
    }).ToList();

tempAppPropModel = (from x in appPropModel
                    join y in webPropModel on
                    //一個比較的參數
                    x.propId equals y.propId into webPropModel2
                    //兩個比較的參數
                    //new { propId = x.propId, dateTime = x.dateTime } equals new { propId = y.propId, dateTime = y.dateTime }
                    rom y in webPropModel2.DefaultIfEmpty()
                    where (y == null) || (x.dateTime > y.dateTime)
                    select x).ToList();

public class PropModelComparer : IEqualityComparer< PropModel >
{
    public bool Equals(PropModel x, PropModel y)
    {
        return x.propId == y.propId;
    }

    public int GetHashCode(PropModel obj)
    {
        return obj.GetHashCode();
    }
}

appPropModel.AddRange(appDelModel.Intersect(webPropModel, new PropModelComparer()).ToList());