It is impossible to do it with Ibus or GNOME, but it is working now with fcitx5 and KDE Plasma 6 if configured correctly. I use other applications based on Electron like Obisidian (which is a Flatpak app), and have no issue with using fcitx5.
The only setup needed on system side is to set virtual keyboard to Fcitx 5 Wayland launcher, so you need to install kcm-fcitx5 in addition to language addons.