text-input-v3 preedit should use text highlight style for text between cursors.
Right now, gtk does not use highlight for text between cursor, but just "bold" for the text. This does not work for certain input method usecase (specifically, some pinyin, mozc). Depending on the font, bold might not even work if user font doesn't have a bold style.
For example, mozc with text-input-v3
mozc with im module: