Sudden drop in battery percentage on iPhone 14 Plus after iOS 17.3.1 update

Apple will not see your post in this user-to-user forum, and further, there is nothing Apple can do about a problem with your phone unless they can see your phone, so make a genius bar appointment→Genius Bar Reservation and Apple Support Options - Apple

But first, how long has it been since the phone was new? That's all that really matters. On average battery capacity will lose about 1% a month from the time the phone was first turned on.