These components are not used inside any Jetbrains IDEs. Those IDEs are, of course, written in Java and cannot use a browser-based UI framework. This is for "our web-based products like YouTrack, Hub, TeamCity, and Upsource" (per the original release blog post for Ring UI). Those products support mobile.
JetBrains IDEs are not on mobile though. It doesn't matter if they're incidentally accessed on mobile if they're not actually designed to be used on mobile.
It's a bug that manifests itself on mobile, but it probably does the same thing on desktop too if you shrink the window really small, and even if it doesn't, it's just a CSS big that is triggered by mobile browsers. There's nothing big that is preventing it from working fine on mobile. Most of the pages do work fine.