2023 4 in to 8 in sync 3 upgrade.

I'm planning to upgrade my 4 in shitty calculator to a 8 in sync 3. From my understanding, it's plug and play from 2019 to 2023. Most videos I've seen are those pre-built kits from various companies. They always mention that they need to use a OBD2 plug in to keep all factory features. My question is, what are they actually programing? As far as I know, it's only activating drive modes to the extra switch you get with the new bezel.