Hi DavidR,
Thank you for getting back to me. FYI, I did turn off Avast self-defense mechanism before trying to set AvastSvc.exe service Startup type to "Manual". I used to be able to do it on my Windows 7 laptop with Avast 18.8. Like I wrote in my last post, the reason for this is because I work (I'm using my computer) mostly OFFLINE so there is no need for the antivirus to run. Another main reason is that I also want to update the default Microsoft Defender's virus definition files once in a while to keep it up-to-date and with the Avast antivirus running, Microsoft Defender is turned OFF so I can't do that.