Here are my settings and is worth keeping an eye on for the next several days on ahead.
Task Scheduler settings:
Start the Task: On System Startup
Repeat Task Every 1 hour

"C:\Program Files\Windows Defender\MSASCui.exe"
-Update -hide

This argument above actually starts the Windows Defender GUI but is always hidden and runs only in the notification area so no windows popup each time.

Like I posted before, I still get the Windows Defender notify for Download notification. Hopefully with the changed settings above will do the trick or should do the trick.