Battery health decreased 2% in few weeks. Is this normal?

Batteries, like people are individuals. No two people age exactly the same and batteries don’t age the same either. The exact usage, chemical makeup, storage conditions, exposure to heat and cold and about a dozen other factors mean that every battery ages differently. Battery aging is not a linear (straight line) and degrades at different rates as the chemicals in the battery age and other factors mentioned above. Apple expects your battery health to be at 80% after 24 months. If your battery health misses that expectation, contact Apple Support.

Please review the Apple Support articles on battery optimization. It contains the best  current practices for battery charging.

iPhone Battery and Performance - Apple Support

Batteries - Maximizing Performance - Apple

About the battery and performance of iPhone 11 and later - Apple Support

If you replaced the battery mid-August, the battery should be at about 96% at this time.

The reason......battery decline averages about 1% a month over longer periods. But, that's an average and the decline is not linear though. For example, the battery might go 3 months with no decline and then decline 3% during the next week.

Lucky you. Your battery is doing better than average.

All that you really need to think about is replace the battery when the Maximum Capacity is down to 80%. Otherwise, you will drive yourself crazy if you are checking the battery all the time.