Does running a laptop while charging damage the laptop?

Laptop is a portable device. If you use a 24/7 plug-in, it is better to use a desktop rather than a laptop. Laptops are used by people so that they can be easily carried anywhere and can be used in batteries for a long time without being plugged in. 

Now let's talk about charges. Lithium ion or lithium polymer cells are mainly used in laptops. Lithium batteries lose some of their efficiency per charge and discharge cycle. You can't turn it off because it's a lithium battery. So the more you use the battery, the faster the battery life will decrease. 

So if you think that if you always use the plug in then the battery will retain its maximum efficiency, but not for long. It is not a matter of keeping the battery production in storage and leaving it unused. So even if you do not use it, the battery will gradually lose its efficiency.  

The only way to keep a good battery is to use it. The battery has been given to the laptop for use. So use the battery when there is no opportunity to plug in. But when the low battery warning comes from the system, try not to use the battery anymore. The battery does not have a chance to be overcharged when it is fully charged after plugging in. A BMS circuit is connected to the battery which provides protection against voltage, temperature, current flow, cell voltage, over voltage, over current etc. of the battery. So when the cells are full, they stop taking automatic charge. 

The modern operating system does another interesting thing that it will show you that the battery is 100% charged but does not actually. Keeps up to 90% of battery life. Apple's laptops are monitored using artificial intelligence to monitor when and how long you are charging the laptop each day. He makes a prediction according to when you can use the battery and based on that it is 90% to 100% full. 

There is only one purpose to inform so much. The laptop itself will do whatever it takes for the battery. You will do your job. You bought the laptop because you need a portable device, so use it anyway.

When operated on a maximum laptop battery, its CPU and GPU are downclocked, display brightness decreases, fan speed decreases, background data fetching stops. This works so that the laptop can give you more backup by consuming less power. But when plugged in, the laptop runs normally, so it can use maximum power if needed. So you clearly understand that you will get better performance if you keep it plugged in while doing heavy work.