Looking at the page behind the create account box in your image, I'd say you're on the US website trying to create an account. You can tell by the "round red A" logo (different from the UK logo), also if you click on either of the app store icons I suspect the app will show KIA America as the developer.
I registered through the UVO app on my phone. There were two options, UVO Account, or KIA Account. The KIA Account option is also where you go to register a new account. However if you already have a myKIA account you can login with that. The UVO account option appears to be for users who had an account registered before 14 Jan 2021. I suspect the most appropriate option for many is the second option, use a myKIA login or create a new account.
In the app, click the KIA Account option, enter your myKIA account details and log in, or scroll down and select Create Account. If you are creating an account, part way down the page there is a drop down to select your country.
This seems to be a pretty accurate guide to the process (bear in mind this guide is for the EU market - possibly Germany, so may have slight variations):
It has to be said that KIA UK documentation is appalling, quite a lot of stuff is undocumented, there are no decent digital manuals available, those that are tend to be cut and paste jobs from other regions or out of date, and printed manuals aren't supplied. When compared to KIA USA offerings, there is the distinct impression the UK is an afterthought.
As an example, this is the UK website, and if you watch the video, it's out of date, showing the old app which no longer bears any resemblance to the current app and login/registration process. Scroll down to the bottom and it does have links to the Android and Apple app stores: