I have this same issue, I bought my iPhone 11 three months back. Most surprising part is when I called the Apple customer care to report the issue that my battery health dropped to 99%, the associate who was assisting me told that is a normal thing for iPhone 11. I was having an iPhone 6S bought in 2016 and the battery health was 100% and in 2018 only it started reducing gradually.
So I would say either iPhone 11 battery is not that excellent as the company claims or battery health is not showing the correct value in the Phone.
PS: I am not an extensive user, I fall in the category of smart phone users who checks their social media stuffs occasionally.