Hi,
I tried your solution and it didn’t work for me. After unchecking and restarting, I still get those journalctl errors and the setting comes back, i.e. unchecking doesn’t stick.
However, when I tried the solution suggested in the link I provided, it works. No more errors in journalctl. So, basically setting “VariantList=basic” in ~/.config/kxkbrc file fixes the problem.
Since you closed the topic, I thought I inform you. You might want to take a second look at this issue and your solution.