The way I understand Konsole under Linux, for "unlimited" scrollback the data
is written to a file (or rather 3 files?), which reside per default in ~/.cache/konsole
Under Fedora it has been that way until konsole5-19.08.3-1.fc31.x86_64.
With an upgrade to konsole5-19.12.1-1.fc31.x86_64 all the setup points are
still there, but there are NO files in the above directory, even with over 2000
lines being available for the scrollback. Anybody knows where they are hiding?

There's another configuration setting for that file location, under (konsole's) Settings > Configure Konsole > File Location. The default is "Use system location" which is under /tmp

Sorry, I shouldn't have said "default", but I changed it to "user cache dir"
so long ago.. So what I meant was:

In my setup (user cache directory) the data is written to ~/.cache/konsole/

And yes, I did check /tmp and there is nothing there either.

George

OK, so I remembered my origins and looked at /proc. It turns out, that the
files are where they should be, but...

15 -> '/home/xxx/.cache/konsole/#5242905 (deleted)'
16 -> '/home/xxx/.cache/konsole/#5242987 (deleted)'
17 -> '/home/xxx/.cache/konsole/#5243086 (deleted)'

... are not there anymore. It seems that to avoid the file hanging around
after the konsole dies strangely, the files are opened, attached to and
then deleted. Of course the program can still use them, but once it dies,
they just go away (no directory entry). It might beat the files lingering
around "after death", but it sure looks strange to a casual user.

Sorry to have bothered you all, George