iPhone 11 Pro only 8 months old yet 86% Battery Health

Hi I bought my iPhone 11 Pro 8 months ago, I have used it normally, charged it as Apple instructs, and have not ever used it intensively (I don’t play games and rarely edit videos or do anything that causes the device to heat up.) And yet, to my surprise, my battery health is already down to 86% and I have noticed my battery drains faster than it used to. This terrifies me because not only was this phone insanely expensive, but I also have no way of paying for a battery replacement or a new phone. I was specifically told by Apple that these phones last a good 3 years, but this is obviously not true. My battery health was at 92% 3 months ago. I truly hope this is just a glitch with the new iOS 14.5 update. Please help