Thanks Felix, Knurpht for your replies. I thought I would report back that the solution was to use mono-spaced character sets. IMHO this is a poor design/implementation of Konsole, it should either outright reject using variable size fonts, or handle them properly. This is a user trap and it took me awhile to find the solution. Hopefully others will find this thread if they encounter the same problem.

    Marc...

Marc Chamberlin via openSUSE Users composed on 2024-01-05 10:53 (UTC-0800):

I have recently encountered an annoying problem on -

marc@wa7pxw:/etc> more os-release
NAME="openSUSE Leap"
VERSION="15.5"

...

with Kconsole that I am unable to figure out how to fix. The "Input 
Cursor" (I don't know what it is called) is being shown at a wrong 
location. Initially it is shown at a position that is quit a ways from 
the end of the line's title (the stuff before the '>' prompt. As I type 
in characters on a line the "Input Cursor" gets further an further out 
front at away from where characters are actually inserted in the line. I 
will try to show what is happening visually below where 'I' is the 
location of the "Input Cursor" -

marc@wa7pxw:~/bin>        I

marc@wa7pxw:~/bin> a I

marc@wa7pxw:~/bin>        aaaaa     I

I hope this survives the text reformatting that is done after sending 
this to the group via email.  Can anyone tell me what is going on, where 
I might have screwed the configuration for Konsole up, or if an update 
clobbered me? I have search as many of the font and icon setting tools 
that I know about, (System Settings, QT5 settings, QKT6 settings)  
perhaps there is yet another tool I should be using? As always, many 
thanks in advance to helping me solve this issue!

I had this happen long ago and don't remember the solution. I do have suggestions:

1-try recreating your font cache, after logging out of Plasma, logging in on a
vtty, and removing the content from ~/.cache/: fc-cache -fr

2-uninstall any fonts you don't use or expect to use

3-ensure the selected monospace font in system settings>appearance>fonts is indeed
a monospace font that is installed

4-try selecting a different monospace font in system settings>appearance>fonts

5-try the same processes as 3 & 4, but in Konsole
settings>profiles>appearance>font for the profile(s) you actually use