Ubuntu – IBus input methods work only in system search

I have just upgraded Ubuntu from 19.10 to 20.04, and suddenly find that I can type Chinese characters with IBus only in the system search (the search bar that appears after pressing the Super key) and Telegram, not in applications such as gedit, Firefox, terminal, and Chrome. In these applications, IBus input methods (ibus-chewing, ibus-pinyin) can only type English characters, and pressing Shift to switch between Chinese and English does not work.

I have tried:

1. following ArchWiki IBus page and adding four lines

   export GTK_IM_MODULE=ibus
   export XMODIFIERS=@im=ibus
   export QT_IM_MODULE=ibus
   export GTK_IM_MODULE_FILE=/usr/lib/x86_64-linux-gnu/gtk-3.0/3.0.0/immodules.cache
   

   in my $HOME/.bashrc; and

2. running im-config and choosing the default configuration.

None of the above works.