Thanks to the help of KDE Edutainment reviewers and community it became possible to port KmPlot away from the deprecated dependencies and fix several nasty bugs.
The fixed bug list (with several showstoppers):
https://bugs.kde.org/show_bug.cgi?id=190860
https://bugs.kde.org/show_bug.cgi?id=210136
https://bugs.kde.org/show_bug.cgi?id=302691
https://bugs.kde.org/show_bug.cgi?id=325627
https://bugs.kde.org/show_bug.cgi?id=360685
https://bugs.kde.org/show_bug.cgi?id=385715
and maybe
https://bugs.kde.org/show_bug.cgi?id=267203
https://bugs.kde.org/show_bug.cgi?id=320394
Hopefully, not many new bugs were added.
Is it possible to bump version from "1.2.1" to "1.2.2"?