The linked article only mentions LibreOffice, Open-Xchange and Linux.
The following article mentions Libre Office Writer, Thunderbird, NextCloud as well as a later switch to Linux. That article explicitly says NextCloud will be used for chats, video conferences and file sharing.
This official site mentions LibreOffice, Open-Xchange, NextCloud, cross-platform APIs, VoIP and a switch to Linux. It says that they generally want to use NextCloud for collaboration.
The linked article only mentions LibreOffice, Open-Xchange and Linux.
The following article mentions Libre Office Writer, Thunderbird, NextCloud as well as a later switch to Linux. That article explicitly says NextCloud will be used for chats, video conferences and file sharing.
handelblatt.de (German)
This official site mentions LibreOffice, Open-Xchange, NextCloud, cross-platform APIs, VoIP and a switch to Linux. It says that they generally want to use NextCloud for collaboration.
schleswig-holstein.de (German)
EDIT: TLDR: they switch to NextCloud Talk