My iPhone 12 is relatively new, gotten around late January/early February.
The iPhone 12 was discontinued in September 2023, so even if your phone was one of the last off the production line, the phone is still 6+ months old and as much as 3 years old depending on when it was placed into service.
If the phone really was "new" when you purchased it in "late January/early February", the Maximum Capacity would not have dropped 8% by February 5th, and another 6% in just one more month.
Things just don't add up here.
Either the phone is really nowhere near as "new" as you thought.....or.....if it is.....the battery is defective and you would want to make an appointment at the Apple Store or take the phone to an authorized Apple service shop to get the battery checked out.
You can find a list of authorized shops in your area using the link just below:
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