IBus input method is working in GTK apps only on Debian testing (bookworm)

I try to get IBus input methods working on my Debian testing (bookworm) under Gnome 43. For example pinyin I installed it with sudo apt install ibus-pinyin When I switch to Chinese now the Chinese input works only in GTK apps but not for example in Firefox or in Electron born apps like Atom or Signal. What could be the cause of this problem and how to fix it? Is this a Debian bug or a specific problem of my configuration?