Presumably the OP's question was to find rows where all columns have the same value???

CROSS APPLY VALUES is definitely the way to go, but your CASE statement made me scratch my head for a while to determine the logic being implemented. To my mind, the following expresses that logic for more clearly.

ymmv, obviously

WITH Mysample (Record_id, Col1, Col2, Col3, Col4, Col5) AS (

SELECT 101, 'A', 'A', 'B', 'A', 'A'

UNION ALL

SELECT 102, 'B', 'B', NULL, NULL, 'B'

UNION ALL

SELECT 103, 'C', 'C', 'C', NULL, 'C'

UNION ALL

SELECT 104, 'D', 'C', 'D', 'D', 'D'

)

SELECT m.Record_id, d.MAXVAL as NewCol

FROM Mysample m

CROSS APPLY (

SELECT MAX(X.Newcol) as MAXVAL, MIN(X.Newcol) as MINVAL

FROM (VALUES (m.Col1), (m.Col2), (m.Col3), (m.Col4), (m.Col5)) X (Newcol)

) d

WHERE d.MAXVAL = d.MINVAL

;