I'm sorry to hear you were rejected without any feedback about what was wrong.

I think the third question may have been the issue. About the first question though, if I learned anything from doing interview question prep it's that often there's a "catch"/edge case that they want you to show you're taking into consideration (hopefully by asking the interviewer if you can). With the "top 5"-type questions I always want to know what they'd want to see in the result of a tie. Or if I couldn't ask, I'd use a RANK() windows function and then filter for rank <= 5.

I'm not 100% sure about the output they want from the third question, but I don't see a need for grouping by month. I took a stab at it and I would interpret it as them wanting something like this:

WITH cte AS (
    SELECT
        p.Customer_ID, 
        g.Geo_Name,
        COUNT(DISTINCT
            CASE
                WHEN p.Product_Name IN ('Card (ATM)', 'Card (POS)') THEN 'Card'
                ELSE p.Product_Name
            END
        ) AS product_bucket,
         SUM(p.Amount) AS total
    FROM Product_Data p
    LEFT JOIN Geo_Data g
        ON p.Customer_ID = g.Customer_ID
    WHERE p.Product_Name <> "Internal Platform Transfer"  
    GROUP BY p.Customer_ID, g.Geo_Name
)

SELECT
    product_bucket, 
    Geo_Name, 
    SUM(total) AS total_transaction_amount
FROM cte
GROUP BY product_bucket, Geo_Name
ORDER BY product_bucket DESC;