https://wccftech.com/oneplus-optimized-charging-feature-promises-to-make-your-battery-last-longer/

One of the fastest degrading components in a modern-day smartphone is its battery. It is, in part, due to shoddy charging practices. Contrary to popular belief, it is NOT healthy to leave your smartphone plugged in overnight. Lithium-ion batteries don't like being left at 100% charge for extended periods, which is why it is recommended that you keep your battery between 20% and  90%. Furthermore, charging at higher wattages is harmful to overall battery life as well. An unhealthy battery can affect overall device performance, as demonstrated by Apple. OnePlus now unveiled a software-based solution called Optimized Charging, which is designed to defer the battery drain rate.

Simply put, Optimized Charging is a software feature baked into OxygenOS. Once your battery is 80% charged, it'll stop there via the new “user sleep cycle detection” function. Your phone will automatically start charging 100 minutes before your daily wake up time, first alarm or custom event. It will take your phone a few days to figure out your 'routine' and adjust the charging time accordingly.