iTunes and iPhone storage settings lie about free storage

My Whatsapp backup couldnt be completed because it said there was not enaugh free space on my phone. When I go into settings it says there are 16.22 GB available, however whatsapp diagnostics said there are 2.46 GB available. Wait, what? So I connected my phone to a pc and iTunes says 15.28 GB (???) and some random app I found online said 2.58 GB which is around what whatsapp said. Why are iTunes and iPhone storage settings lying about storage usage and giving false numbers? Keep in mind my phone is less than a month old and on the latest iOS 13.2.2.