fcitx-frontend-gtk3 binary package in Ubuntu Jammy s390x

 Fcitx is an input method framework with extension support, which provides
 an interface for entering characters of different scripts in applications
 using a variety of mapping systems.
 .
 It offers a pleasant and modern experience, with intuitive graphical
 configuration tools and customizable skins and mapping tables. It is
 highly modularized and extensible, with GTK+ 2/3 and Qt5 IM Modules, support
 for UIs based on Fbterm, pure Xlib, GTK+, or KDE, and a developer-friendly
 API.
 .
 This package provides the GTK+ 3 IM Module frontend, which is
 recommended for all desktop users. This is the best solution if you are
 looking for a better input experience with GTK+ 3 applications.

Source package