linq.cs

var orders = new List<Order>
{
    new("Order 1 -10 itens", GenerateOrderLines(9)),
    new("Order 2 +10 itens ", GenerateOrderLines(12)),
    new("Order 3 +10 itens", GenerateOrderLines(18)),
    new("Order 4 +10 itens", GenerateOrderLines(22))
};

List<OrderLine> GenerateOrderLines(int quantity)
{
    var result = new List<OrderLine>();
    for (var i = 0; i < quantity; i++)
        result.Add(new OrderLine($"Product {i}", i, i));

    return result;
}

var data =
    from order in orders
    let totalItems = order.OrderLines.Count
    let total = order.OrderLines.Sum(x => x.Price)
    where
        totalItems > 10 &&
        total > 100
    select order;

foreach (var item in data)
    Console.WriteLine($"{item.Number} - {item.OrderLines.Sum(x => x.Price)}");

public record Order(string Number, List<OrderLine> OrderLines);

public record OrderLine(string Product, int Quantity, decimal Price);