Corrected version without a scalar function
😎

DECLARE @m NVARCHAR(max)= N'\u0633\u0644\u0627\u0645'

;WITH T(N) AS (SELECT X.N FROM (VALUES (0),(0),(0),(0),(0),(0),(0),(0),(0),(0)) X(N))
, NUMS(N) AS (SELECT TOP(LEN(@m) / 6) ROW_NUMBER() OVER (ORDER BY @@VERSION) AS N FROM T T1,T T2,T T3,T T4,T T5,T T6,T T7,T T8,T T9)
SELECT
(
  SELECT
   N'' + NCHAR(CONVERT(INT,CONVERT(VARBINARY(MAX),CONCAT(N'0x',SUBSTRING(@m,((NM.N * 6) - 5) + 2,4)),1),0))
  FROM NUMS NM
  FOR XML PATH(''),TYPE
).value('(./text())[1]','NVARCHAR(MAX)') AS STR_VAL

Output
????