Why is my brake light is still on when car switched off

First suspect is the brake switch on the brake pedal. When you look at this issue at least 7 out of 10 end up being due to a faulty switch that is stuck on, or it is out of positon and always being pressed. While this video is for a 2013 Sonata, the procedure really doesn't change much between generations - just the part and connector. This video shows how to do it: https://www.youtube.com/watch?v=JGKztRYi...

You can get the part here: https://www.kiapartsnow.com/genuine/kia-... -- US Georgia

https://www.kiapartsnow.com/genuine/kia-... -- SK factory

NOTE: I sourced it from Kiapartsnow for an Optima - the Optima and Sonata are the same platform, but the Kia is more targeted towards younger drivers then the Sonata. Sonata=Old folks, Kia=young folks

The part appears to be the same between the two for this but the reason for the variation is some parts are different between the cars. It's not much of anything as I have done the search before between them for an Optima, but the designation means you should probably check your VIN plate in the door to see if it says Georgia or South Korea.