rune brew install codex
give him the instruction md file.
Good luck!
Welcome to universal blue 
How to set up Fcitx5 is in documentation: Frequently Asked Questions | Bluefin. Just skip the GNOME extension step if you are using KDE.
If you have issues with the input panel, see official documentation: Using Fcitx 5 on Wayland - Fcitx
Already tried this … not working.