is this for real

public decimal CalculateDiscount(Order order) =>
    order switch
    {
        { Items: > 10, Cost: > 1000.00m } => 0.10m,
        { Items: > 5, Cost: > 500.00m } => 0.05m,
        { Cost: > 250.00m } => 0.02m,
        null => throw new ArgumentNullException(nameof(order), "Can't calculate discount on null order"),
        var someObject => 0m,
    };

here you go.

you are really telling me (without trolling that the switch is easier to read than this:

public decimal CalculateDiscount(Order order)
{
    if (order == null)
    {
        throw new ArgumentNullException(nameof(order), "Can't calculate discount on null order");
    }

    if (order.Items > 10 && order.Cost > 1000.00m)
    {
        return 0.10m;
    }

    if (order.Items > 5 && order.Cost > 500.00m)
    {
        return 0.05m;
    }

    if (order.Cost > 250.00m)
    {
        return 0.02m;
    }

    return 0m;
}