A bug was introduced in ScummVM core a few months back, text input is impossible and there are games where typing with a keyboard is unavoidable; Game Focus doesn’t make any difference. There is currently an open issue discussing this bug: https://github.com/libretro/scummvm/issues/176
According to user @diablodiab:
behavior of RETRO_ENVIRONMENT_SET_KEYBOARD_CALLBACK has been changed so that for some platforms you are no longer provided with the character code of the key that was pressed. Instead it seems you have to rely on the provided keycode.
He has provided a workaround by compiling a fixed version of the core, but unfortunately it is not compatible with RetroArch v1.9.1+
I’m hoping that a libretro dev, like @Twinaphex or @jdgleaver, gets a chance to tackle this and a few other bugs that have nagged this core for a while now.
Thanks.