Distinct Count with Group By in SQL Server

Hello Everyone,

I have this code that I count a field in my SQL and I have a specific column which I need to count distinct the values but I don't know how to use it in this format

This is the code :

SELECT
        Sum(Price) As Total,
        CONVERT(char(7), date, 120) As [year],
		Department ,
		 Sum Dinstict (CONVERT(INT, CONVERT(VARCHAR(MAX),quantity))) as Lesh
    FROM
        dbo.Expenses
    WHERE
  CONVERT(char(7), date, 120) Between '2020-01' And '" 2020-07"' AND
        Department = 'FixCost' 
    GROUP BY
       CONVERT(char(7), date, 120),
	   Department 
	   )
SELECT
    Total,
     [year],
	 Department as 'Department',
	  Concat(SUM(Convert(int,Convert(Varchar(MAX),(Lesh)))) OVER (),'') As GrandTotal
FROM
    cte
WHERE
     [year] Is Not Null

What I have tried: I need to use it here :

tal,
[year],
Department as 'Department',
Concat(SUM(Convert(int,Convert(Varchar(MAX),(Lesh)))) OVER (),'') As GrandTotal

I tried this, but it doesn't work :

Concat(COUNT(Convert(int,Convert(Varchar(MAX),(Distinct,Lesh)))) OVER (),'')

Thank you, Blessings