You can have CarPlay set up to either take up the full screen or be in split screen. With the phone unplugged, you have to go to setup > device connections > phone projection/CarPlay. If you have the box that says “use split screen” checked, CarPlay will be in split screen with 1/3 of the screen being the Kia interface. If you have that box unchecked, then CarPlay will take up the entire screen.
Android Auto, on the other hand, is a different story. As far as Kia’s software on these widescreen displays is concerned, there is no widescreen Android Auto. So it doesn’t look for it and places AA in a box in the classic aspect ratio. So at this time, if you’re using AA, you really want to go into the setup > device connections > phone projection/AA and make sure you check “use split screen” to display the Kia split screen UI, because otherwise you will be wasting that right 1/3 of the screen. And then continue to hope that Kia will fix this with a future update… but be aware that many updates have come and gone since widescreen AA was introduced in late 2019, and Kia’s software still doesn’t look for it.