Why do you want to schedule it to power off?
Otherwise if you're referring to schedule restarts you can do so by going into: settings - battery and device care - three dots on top right - automation - restart at set times
You'll be able to customise when you want your tablet to restart.
It gets used in a situation where it could left for weeks without usage.
I want to protect the battery by having it shutdown each night so if it is left the battery does not run totally flat.
I know I can do it by rooting the device and automation software but I want to avoid rooting the device ...