There are several things to investigate.  The remote site is one of the first things to look at.   Do they perhaps have any new web security methods in place?   Things...

FOR XML PATH(''), TYPE has to follow the end of the query.  It can't be within the SELECT.   Has to be at the end of the query...

Does that object have any kind of "close" method?   You might  need to do that to disconnect from the remote site.  Not doing so risks controls on the remote site...

Okay, question 1). Why create the jobs on the secondary at all ?   You are seeking to not have them run...
Question 2.) See question 1.

That depends on your desired value.   The median value computed by PERCENTILE_DISC has to actually come from the data, so the number of values is irrelevant in that regard only. ...

This might be as simple as this:
DECLARE @ntop AS int = 3;

WITH RAW_DATA AS (

    SELECT
        DB                                AS DatabaseName,
        [proc]                            AS ProcedureName,
        [date]                            AS TheDate,
        MAX(TTExec)                        AS MaxExecutionTime
    FROM YourTable

Not that I'm aware of.   If you have an SSIS package that uses environment variables for configuration purposes, generally, that is the kind of thing that tells you what your...