If I understand the desired logic correctly, then this:

alter table [DMPCRU].[dbo].[VaspianCalls] add [Hold_Time] as (iif(Duration < '00:52', '00:00', Duration))

Look at the query plan.  Is SQL able to do seeks to find the 1000 rows or does it have to scan the whole table first?

I thought there were settings for source and destination schema.  It defaults to dbo, but afaik, the two schemas do not have to be the same.

MS has a built-in standard report for Top 10 Avg or Total CPU queries, but that is a point-and-click, and I don't know of any way to store the results.

If you don't genuinely need RowNum and TotalRowNum, drop them.

If you do, you can pre-compute RowNum in the X1 table, and compute the TotalRowNum based on the pre-computed RowNums in...

There's really not a better way.  You'll need to repeat the column list for both the inserted and deleted tables for any method you use.

I'd use CROSS APPLYs to assign alias names to make the main SELECT statement and conditions easier to read and maintain.  For example:

--...prior code same as before...
DELETE...

I'd use a function.  You don't have to put in every db, you can call a function from another db.  Let's say you created a "Shared_Functions" db to store the...

Interesting.  It seems as if there is no variable data at all on a row, the entire "variable data" section of the row header is left out.  But when the...

The 2 bytes for varchar len are always present, even if the column is NULL.

NULL itself is set as one bit per column, i.e., a "NULL bitmap".  Every column will...

Maybe try CASTing to an explicit length?:

,CASE 
WHEN T.[PD_ID] in (@Part)
THEN CAST('PD_ID_Match' AS varchar(30))
WHEN T.[Flat_PD_ID] in (@Part)
THEN CAST('FLAT_PD_ID_Match' AS varchar(30))
WHEN T.[Like_PD_ID] in (@Part)
THEN CAST('Like_PD_ID_Match' AS varchar(30))
WHEN T.[Flat_Like_PD_ID]...

Off the top, just streamline it as much as you can:

BEGIN
    RETURN (
        SELECT product = CASE...

What row was just FETCHed from, that is the row that SQL will delete, since that is the current position of the cursor.

Don't force SQL to fully reprocess the conditions before DELETEing each row, instead use WHERE CURRENT OF in the DELETE:

DECLARE @user VARCHAR(50)
DECLARE @role VARCHAR(50)

DECLARE db_cursor CURSOR LOCAL...

;WITH
cteTally10 AS (
    SELECT * FROM (VALUES(0),(0),(0),(0),(0),(0),(0),(0),(0),(0)) AS numbers(number)
),
cteTally100 AS (
    SELECT ROW_NUMBER() OVER(ORDER BY (SELECT NULL)) AS number
  ...