Thank you very much Luckyh!
I am the author, and the article is the result of Bug 41211 and related to the (german) thread UCS für Blinde: grub serielle Konsole konfigurieren, back in 2016.
Unfortunately, I can’t edit this kb article, it is not allowed anymore. Maybe someone from Univention support could update? (or allow to edit this article: It would be a pleasure for me to contribute and to keep the article up to date)