Yellow screen on iPhone 13 Pro Max after iOS 18 update

Try rebooting your iPhone, here’s how to do it: Volume Up, down and then press the right button tight until the Apple logo appears, do the procedure without touching the screen. After that you can release the button and wait the phone to boot up again.

Also it’s important that you adjust your display settings going to “Display & Brightness” > “True Tone” and anything that effects your display in such a way and turn them off, it’s so just in case if you try updating your phone, the same problem won’t happen again, but I’d personally recommend just turning the True Tone off :)