How to enable LED notifications on Pie
There is a settings option called "Custom Restrictions".  I had to search the settings (from the search bar) to find this, but it didn't indicate where it was in the menu structure.  Under "While the screen is off" de-select the option that says to not blink.  If you do not see this option (as I did not) then you do not have a notification LED on your phone (shocker, I know!) and that is the reason you can't get the LED notification working.