Apple still provides older iOS devices that only run version 12 with updates. The latest update brings the version number to 12.5.4.
This closes security holes that could lead to malicious code being executed via a website in the browser engine WebKit. Furthermore, a problem was solved that would have allowed the execution of arbitrary code via a false certificate. So an update to this version is strongly recommended if you – and this is very likely – are using these devices on the Internet.