Laptop battery wear after 7 months – is this normal? (My laptop is Predator PHN16-71 53M7)

I've been using my laptop for about 7 months. I always keep the device cool, even while gaming (I use a cooling pad, good thermal paste, and clean the internals regularly) and when playing heavy games, the GPU temperature stays between 50–80°C, and the CPU temperature ranges from 60–90°C. . I also usually keep it plugged in while working, and limit the charge to 80%. Recently, I checked the battery status using Windows Battery Report, and here are the results:

• Design Capacity: 90,090 mWh
• Full Charge Capacity: 81,728 mWh
• Cycle Count: 21 charge cycles

This means the battery has already lost around 9.3% capacity, even though it's only gone through 21 cycles.
The battery is made by Panasonic, model AP21A5T, and it's a Li-ion type.

My questions are:

• Is it normal for the battery to lose almost 10% capacity after just 21 cycles and 7 months of use?
• I’ve always kept the laptop cool, never letting it overheat, even under heavy load.
• Could it be because I leave it plugged in most of the time?
• Try battery calibration?

If anyone has experience with battery care, please share how to extend battery life effectively.

If the battery continues to degrade, should I send it in for warranty service (it’s still under warranty)?

Thanks in advance for any insights or recommendations!