ok, I got it to work…
uninstalled and removed all of owncloud client
searched for any remaining files containing loud, nothing found
reinstalled owncloud-client
still got the same version 2.4.1
uninstalled …
now I looked into the processes and identifed that there is still a owncloud process running - killed it.
now it was really clean.
installed via apt the client and voila it is now on version 2.5.4.
It seems that apt remove did not stop the old process, so the new installation never started as the old was still running.
No clue where the old version came from as I have never installed any owncloud client before on this machine. it was the very first time…
one thing is coming to my mind, when adding at the very beginning the apt keys to the system, I copied on the first attempt 19.04 instead of 18.04. I realized that and fixed it. do other version use an older client? may needs checking