Thanks for the info!
That's funny. Installed the trial, got too many drives, installed the bought key. tried ssh (not working). After that docker, installed the the ssh config tool to get ssh support, installation without any problems, but it said "ssh daemon not running", tried to start it, no error messages, nothing - some other people seem to have the same problem if you google for that tool, so ssh does not seem to work for "everyone else" - uninstalled it.
Didnt' came to the ppk stuff as standard ssh was not working and the keyboard.
So after your answer it is a configuration problem or bug that occurs only on a few systems. I look into it, hope that Slackware is not too different from Debian/Ubuntu which I am used. Maybe someone can give me a few hints regarding where too look. Atherwise I just google it out and post the results/solution here and direct to the devs.
TNX!