Comment 18 for bug 1851573

The error message clearly states, that kde tries to write to a file in the root directory of the system and not in any home directories.

Let's track down where the $HOME variable substitution gets lost in between.
Attached we see an other flavor of this message with only one slash where a tilde or path to the home directory should be visible:
[1] kde-debconf-helperrc.jpeg