My battery doesn't ever drop at night. I do what Apple recommends and my phone is on it's MagSafe Charger when I go to bed, every night, all night. My phone backs up nightly and is ready for a full days use in the morning, with Optimized Battery Charging on.
I would, however, expect a brand new iPhone, which isn't plugged in at night to lose some charge, maybe even more charge initially as it indexes all the billions and billions of bytes of data on the phone. Other things which could be eating the battery at night is what you've got it set as far as cellular. If for example, you have it set to 5G always and 5G isn't very strong in your house, the phone will work VERY hard to find a good cellular connection, which can chew up the charge in the battery. How many of your apps have you granted location access to? Location Services can adversely affect battery life. There are a lot of variables at play.
Honestly, you should plug your phone in at night and wake up to a backed up phone, ready for a full days use. And this
is exactly what Apple recommends you do.
BTW, following Apple's charging advice the iPhone 14 Pro Max I just traded in on the 15 Pro Max still had a Battery Health reading of 100% after a full years use.