Any way to get my kindle fire to either turn off or stop using power after a predetermined time like other devices allow? ?

Low power mode does little and if the device is not manually powered off, it still uses power even after the display sleeps as if it were still being used. Is this by Amazon's design?

Marvinator2020-10-30T17:20:10Z

yes, I beleive this thread addresses setting it to auto power off. 
https://www.reddit.com/r/tasker/comments/ajpihi/auto_shutdown_on_kindle_fire_hd_2018/