There are many Powershell scripts for Microsoft Teams available to set different options like GPU etc. including to set Teams as Chat App. So, to activate Teams as Chat App should be simple, but unfortunately not. The scripts all work after schema F, but that doesn't work with the Chat App function. When moving from Skype the Instant Messaging (IM) Integration of Teams is important, for instance to see within Microsoft Outlook if someone is online right now. To help users and the helpdesk, this option should be set during logon by a Powershell script, but how?
The search and analysing of the problem took some time, but at last a small hint on the internet lead to the solution. Next, to make changes in the desktop-config.json file, additional registry values must be set. Only when both things are done, the Teams Chat App integration will work. In the Powershell script, the following lines are necessary:
Other than that, you can use the Powershell scripts available on the Internet. If you like to have my script, then simply drop me an email.