WD periodic scanning turned itself back off,but today it's back on again.
Yesterday it wouldn't stay on unless I disabled Avira, the icon was still in the system tray but hover gave a tooltip that said it was turned off. Turn it back on, it would turn off again after a short time. I was able to update it - it wasn't auto-updating - and start an on-demand scan, but it shut down before it completed. Disabled Avira, then I was able to complete a scan. Then tried to do a startup scan, another feature it has, but that failed.
But today, as I said, it's back on, and it's staying on. But how to schedule scans? There's no clue - but a quick search revealed you have to use the Task Scheduler for that. It sounds like there's some sort of default scanning plan, but no hint what that is exactly - https://www.bing.com/search?q=windows+defender+scheduled+scans&form=EDGEAR&qs=AS&cvid=0e72f3fbe59e4f348335b99df494a72a&pq=windows defender scheduled scans
Much as I despise the Windows Task Scheduler, I managed to do it. I've set up weekly scans, starting tonight - we'll see if they work.
I think it's more trouble than it's worth.
I forgot to mention, I use the built-in firewall but I use a program to provide a UI for it and harden it's settings, called Windows Firewall Notifier. MajorGeeks has a few of these type programs, but this is the one I found I liked best. The current Windows firewall works well enough, but there's no reasonable way to control it. This program fixes that and is very lightweight.