Starting with macOS 10.15.5 Catalina, Apple introduced a battery health management feature that improves your battery’s lifespan by keeping your computer from charging to 100% if it suspects you will be leaving it plugged into power. It is enabled by default but you can turn it off in System Preferences > Energy Saver > Battery Health. This applies only to Mac computers with USB-C, with the exception of the 12-inch MacBook.
One thing to be aware of with battery health management is that it might cause your MacBook to display “Battery Is Not Charging” in the battery status menu even when it’s plugged in. That’s normal, and it’s nothing to worry about. However, if you see that message when your battery is low, it’s a hint that you may not be using the proper power adapter and cable or that the power source isn’t delivering enough juice.