It opens a dialog to install (QApt) and when you click on Install, it asks for password.

Continuing to operation shows DONE, but actually it installs nothing.

Using terminal does not have the same problem.

Eg. download google-chrome and click on .DEB file to install and proceed with the next steps. It won't be installed.

Type: dpkg -i google...... and it installs without any problems.

using systemsettings -> file associations you need to determine the exact command being used to open .deb files and then use that in Konsole to see if there's errors generated

if you have package gdeb-kde you could try right click a .deb -> open with -> other -> gdebi-kde -> click remember -> click ok

Thank you for your answer. I checked file associations for DEB and this is registered: qapt-deb-installer

Doesn't this work? I did not change anything related to this after out-of-box.

don't run a deb distro so can't say

does qapt-deb-installer work ok in Konsole?

Unfortunately no...

are there errors? try re-installing all qapt related packages

also try gdebi-kde as describes in my first post

Yes, it solved my problem thank you, but I will create a bug report for this in Kubuntu...

I reported a bug regarding to this. This was causing if the folder name is non-ASCII

Bug #316187