SELECT highest quantity in related table, exclude if there is a tie
It's a bit unclear what you want, but you can use rank() to collect duplicates, and then another window function that counts those, and filter them out if there is more than one:

SELECT qty.Id 
     , qty.Product_Name
     , qty.Product_Type
FROM (
    SELECT qty.Id 
     , qty.Product_Name
     , qty.Product_Type
     , COUNT(Rnk) OVER () as cnt
    FROM ( 
        SELECT td.Id, prd.Product_Name, prd.Product_Type
        ,  RANK() OVER (PARTITION BY prd.Receipt_Number 
                        ORDER BY prd.Quantity) AS Rnk
        FROM Transactions td
        JOIN Products prd
            ON prd.Receipt_Number = td.Receipt_Number
        WHERE prd.Quantity &gt; 1 
    ) qty
    WHERE qty.Rnk = 1
) WHERE cnt = 1;


If you want the rows, but with null instead of values you can use a case expression:

SELECT CASE WHEN cnt = 1 THEN qty.Id END 
     , CASE WHEN ... qty.Product_Name ...
     , ...
FROM (
...
);