Great tip! I confirmed this on my Pi 400, having it hooked up to a terminal and watching the linux system do a shutdown! One can confirm the Pi 400 has been shut down completely when the green light goes off. I'm going to guess/hope most Pi 400 users would use that sequence rather than pulling the power supply.
I also used this command (
last -Fxn2 shutdown reboot) to see how the last 2 restarts were done. It's a little confusing, but it's another way to check the system if you have console access or ssh.
from - https://access.redhat.com/articles/2642741
A graceful shutdown would show up as a reboot line followed by shutdown line, as in the following example:
# last -Fxn2 shutdown reboot
reboot system boot 4.18.0-80.el8.x8 Mon Aug 31 06:33:11 2020 still running
shutdown system down 4.18.0-80.el8.x8 Mon Aug 31 06:33:01 2020 - Mon Aug 31 06:33:11 2020 (00:00)