This is the One UI 5.1.1 update that's why the size is so big. Samsung doesn't change the version for the S series though but the update includes the latest features. Only foldables and tablets get the 5.1.1 version number. Weird policy 🤷�♂️
Samsung has released a new update package to the Galaxy S23 series, shortly before it delivers One UI 5.1.1 and its first One UI 6 Beta. While this month's update is said to only bring new security patches, it is still roughly a 1.3 GB download.