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.
It doesn’t say what they’re replacing teams with
They go back to Skype for Business.
Skype is done, RIP Skype
The worst chat app I’ve ever used. Impressively bad
They mentioned a german video conf. solution. I’m quite confident it is opentalk.
NextCloud Talk is also German and in other articles it’s said they 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