Hi @D D ,
I was also looking for the MP a couple of weeks ago and because I couldn't find it, I ended up creating one myself.
Most file or folder related operations are very easy to do cover using Powershell. So, I wrote a simple PowerShell script, which did what I wanted it to (Check for the presence of a file in a specific folder). I then used the PowerShell MP from Cookdown and integrated my script in SCOM.
PowerShell Authoring
https://www.cookdown.com/scom-essentials/powershell-authoring
This same link contains also a video with an example on How to integrate every PowerShell script. In my opinion you can very easily cover the scenraios you've listed with Powershelll:
Whether the files count is too high or too low
Whether the total file size (in kilobytes) is too high or too low
Whether the file’s recent date modified is too old
PowerShell – Count Files in Folder using Get-ChildItem
https://shellgeek.com/powershell-count-files-in-folder-using-get-childitem/#:~:text=To%20get%20count%20files%20in,count%20files%20in%20a%20folder.
Get Folder Size And File Count Using PowerShell Examples
https://www.improvescripting.com/get-folder-size-and-file-count-using-powershell-examples/
How to find the file modified after a certain date using PowerShell?
https://www.tutorialspoint.com/how-to-find-the-file-modified-after-a-certain-date-using-powershell
Those are just a couple of examples, there are of coourse many more out there.
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(If the reply was helpful please don't forget to upvote and/or accept as answer, thank you)
Regards
Stoyan Chalakov