An older thread was left unsanswered and closed, and search engines aren’t working properly.
So I will post an answer as a separate thread, hoping that it will get indexed and will help others.
It’s /org/freedesktop/ibus/engine/typing-booster/wordpredictions. Can be changed in dconf-editor, or with gsettings set org.freedesktop.ibus.engine.typing-booster wordpredictions false