Battery life MacBook Air M1 2020

It may be due to the following (in case you aren't aware of this option): If Optimized Battery Charging is turned on and your MacBook Air is used frequently while it is plugged in, pausing the charging at 80% is normal and is a good thing. See: https://support.apple.com/en-md/HT212049

Glad to hear that; mine is sitting at 80% right now also and that's a good thing.