My ipad mini 5 bought in March 2020... Just a month old... doesn't c

This is a battery management feature designed to extend the life of the battery. Keeping the battery charged to 100% 24 hours/day apparently chemically damages the battery. iOS will determine your typical use pattern and is supposed to only charge to 100% in anticipation of your use. Since you don’t use it at night, charge is limited to 80%; then, when your anticipated high-use time approaches it charges to 100% You used to be able to disable this feature; I just checked my iPad Mini5 under iOS 14.2 and that’s no longer an option.