Here and here I have found that the keycode for Capslock is 66. From here I've got the command to remap Caps Lock as Delete:

xmodmap -e "keycode 66 = Delete"

After testing that it worked I have made it run at startup by creating the file ~/.config/autostart/capslock-delete.desktop (based on last link) with the lines:

[Desktop Entry]

Exec=sh -c 'xmodmap -e "keycode 66 = Delete"'

Name=capslock is delete

Terminal=false

Type=Application

It may happen that the Capslock key continues to trigger lock-uppercase beside doing delete. It needs to be disabled as said here, or in KDE, under keyboard settings - Advanced - Capslock behavior - Disable...

Update:

In case the solution of the said above desktop file or command to run at startup is not working, following this answer, this seems to work in Kubuntu 22.04:

• create a file ~/.Xmodmap containing the keycode setting: keycode 66 = Delete

  
  



• create a script like for example ~/bin/capslock.delete.sh:

  
  

   #!/bin/bash           
  
  sleep 1;               
  
  echo "running xmodmap" 
  
  xmodmap ~/.Xmodmap   
  
  

  
  



• make the .sh file executable

  
  



• add the same script file to be executed at startup

  
  

In case one still wants a key or key combination to lock the upper keys (the CapsLOck key default behavior), the following command - involving xdotool - which can be associated with shortcut like Super+CapsLock or Alt+CapsLock) - will do:

xdotool key Caps_Lock

Install xdotool:

sudo apt install xdotool

I have associated Alt+CapsLock with the command sh -c 'xdotool key Caps_Lock'.

One would expect that xdotool might be used in the first place to get the delete action with a command like:

xdotool key Delete

but that doesn't seem to work very well, as said here; I have been able to use it - sort of - with Ctrl+D, but that only deletes text to the right without deleting files. A good alternative to get the delete action (as well as others that I haven't tested) is to use AutoKey, described here, about the delete action: