(Sorry if the label is wrong, it was the closest I could get)
The gist of my problem is that I had a setup with a colemak-dh wide keyboard and a Chinese one, and for some reason the colemak-dh wide layout is no longer showing up in the KDE keyboard menus (and just defaults to typing qwerty). It also seems like I can’t change keyboard layouts anymore either. Help is appreciated.
Well, (assuming you are using X11) i don’t know what you have tried, however there is the usually good Arch Wiki:
https://wiki.archlinux.org/title/Setxkbmap
The manual pages:
man setxkbmap
man xkbcomp
you could also try editing the keyboard file in /etc/default :
sudo nano /etc/default/keyboard
CTRL + o (enter) to save
CTRL + X (enter) to quit
edit: added the ‘assuming you are using X11’ part)