Thanks @Rosika ,
The main point is that “problem solved”, but I suggested trying a non-existetn package.
I live in my Debian ecosystem, and here libdvdcss2 is the package that contains the stuff necessary to decrypt the factory scrambled DVD.
laco@DellG3:~$ apt search libdvdcss2
Rendezés... Kész
Keresés a teljes szövegben... Kész
brasero/oldstable 3.12.2-6 amd64
CD/DVD burning application for GNOME
kylin-burner/oldstable 3.0.9-1 amd64
CD/DVD burning application for UKUI
libdvdcss2/oldstable 1.4.3-dmo1 amd64
Simple foundation for reading DVDs - runtime libraries
That’s why I assumed Ubuntu should have a similar named component, my assumption was clearly wrong.
Seems, Ubuntu put this thing in libdvd-pkg (?? or whatever) package.
I suggested libdvdcss2 because the symptoms (distorted image, and audio) is very typical.
I have no idea about Kaffeine, I never used it.