As mentioned by siggemannen in their comment one method would be to use LAG to check the prior value. To avoid repetition of the OVER clause I use the WINDOW clause here, however, if you aren't on 2022+ you'll need to explicitly define the OVER clause for each LAG function.

SELECT CASE V.Acc_no WHEN LAG(V.Acc_no) OVER Prev THEN NULL ELSE V.Acc_no END AS Acc_no,
       CASE V.VPN WHEN LAG(V.VPN) OVER Prev THEN NULL ELSE V.VPN END AS VPN,
       CASE V.VPN_Count WHEN LAG(V.VPN_Count) OVER Prev THEN NULL ELSE V.VPN_Count END AS VPN_Count
FROM (VALUES(12345678,'abc@ybl',4),
            (12345678,'bcd@ybl',4),
            (12345678,'cde@ybl',4),
            (12345678,'def@ybl',4))V(Acc_no,VPN,VPN_Count)
WINDOW Prev AS (PARTITION BY Acc_no ORDER BY VPN, VPN_Count);

db<<>fiddle