Parameter in where clause not working (where <column> in)

HI all,
I'm having an issue that is normally very simple; but I'm missing something here. I'm passing a simple comma dilimited string into a VarChar(MAX) parameter.  I'm then replacing the ',' with ''',''' in order to have the proper syntax to pass into the Where <colomn> not in @parameter.  

So I have a string:
AA660304-BE86-4C85-ABB6-EC62E15106D5,BC2B3858-CFD1-46E8-9E6D-F6E50DE4FADD

I obviously need to change the commas to include an appostraphe on iether side.
I can see that it does; but the parameter doesn't work.  If I do a select on the paramter after passed in I see that the syntax is correct; and when I use the resulting value of the parameter after the REPLACE FUNCTION, by copy/pasting it into the where clause it works.  

DECLARE @ExludeCategory VarChar(MAX) = 'AA660304-BE86-4C85-ABB6-EC62E15106D5,BC2B3858-CFD1-46E8-9E6D-F6E50DE4FADD'

SET @ExludeCategory = CHAR(39) + REPLACE(@ExludeCategory,',',''',''') + CHAR(39)
SELECT
      P.SADDR1            [Name]
      ,p.HMY
      
      ,SUM(CASE WHEN (W.DATE_Completion IS NULL) Then 1 ELSE 0 END) AS [Total Open]
            
FROM ORDERED W
      INNER JOIN PERSON P ON P.HMY = W.PHMY
      
WHERE (W.DATE_COMPLETION IS NULL)
      AND ((SELECT COUNT(*) FROM CATEGORY_ASSOC CA
                  WHERE (CA.WID = W.WID) AND (CA.CID NOT IN(@ExludeCategory))) > 0 )
      
GROUP BY P.SADDR1, P.HMY
ORDER BY P.SADDR1