I observe my iphone and iPad to only turn off and start up during night, if in normal mode. That's irrespective of being plugged in or not. There is no such behaviour in low power mode.
Solution: put your handhelds in low power mode before you go to sleep.
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iPhone XR, iPad Pro 11", latest OS
Solution: put your handhelds in low power mode before you go to sleep.
,
iPhone XR, iPad Pro 11", latest OS