Depends. Some companies are rather paranoid about privacy issues and using services like Slack or GMail is a clear liability risk, especially when discussing customer data or confidential information. I'm not sure what the GDPR has to say about this but my understanding is that some privacy experts consider services like Slack problematic.
However this depends on the scale and type of company. In practice many smaller companies don't even have a Betriebsrat despite fitting the requirements. I'm also sure not everyone is aware of the details of legal requirements around privacy if it isn't the core of their business and some are even blatantly unaware of basic labor rights.
Some companies do use Slack but I know several examples where the introduction of Slack was prevented for compliance reasons. If these reasons are sound I cannot tell, but dismissing this argument as laughable doesn’t hold either.
I'm at SAP (and in Germany, too), and our team was migrated to Slack Enterprise Grid just this week. We migrated to Slack (from internal IRC) a bit over a year ago and because a lot of other teams did as well, corporate IT was pushed into investigating company-wide Slack as an option, which now became available in January.
Compared to other tech companies, it took us longer to adopt Slack on the company scale, but mostly because Slack was lacking an on-premise solution until recently.
Doesn't the SEC take a dim view of chat programs being used on Wall street? My understanding is that they have to use chat programs with builtin compliance regimes to avoid insider trading and such...
Digital innovation is happening in a lot of sectors. Healthcare and others have privacy concerns that turn a lot of 'efficiency' dreams on their heads.
Companies do use Slack and other similar services