Company unions aren't permitted. But there's an element of this approach in the most recent approaches to undermining unions, where companies create groups for worker voices including ESG and DEI initiatives. I'm not saying companies doing this is necessarily bad, just being descriptive about that at least part of the motivation is to undermine union organizing, as even corporate lobbying groups describe it:

https://theintercept.com/2022/06/07/union-busting-tactics-di... https://www.levernews.com/fear-and-loathing-among-the-union-...

As far as whatever is done in Germany, I can't speak to that since it's outside my area of knowledge.

When / how ?

The European model, as I understand it, is that unions have elected representation on the board of directors for the company in question.

Once the union is established the model they're talking about gives the union a seat somewhere in the executive levels sometimes several on the board. It brings the union directly into the decision making process earlier so there's more chances to address things before they rise to the level of a strike. It could be used to co-opt the union but it doesn't inherently compromise it.