Hi, Are you experiencing problem under WAYLAND? I can't input Japanese for browsers but I can input to terminal console.
It seems some software are not compatible. Please use standard GNOME and Debian provided software. I really can't support others. If you know exact flag to use, please let me know. See all merged bugs under: non-GNOME desktop not supported well by ibus https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=813111 Osamu