No, you're wrong. The people writing the German app in that thread specifically say that they targeted Android/Apple because they had limited time and that they plan to support other platforms in future.

The white label app is a demo. It's not the only possible app. There's no hard requirement stating that all future apps will have to follow it exactly.

So yes, at present the apps that been shown require Android or Apple. But no, that's not definitely going to be the case going forward.

I'm not claiming this is ideal and it may take pressure to ensure that other apps get written. As you say, there's a legal basis for applying this pressure under the DMA and it's highly likely that people will step up and do that.

But this focus on the current apps being Android/Apple based is a distraction. There's a lot to criticize here but this isn't the right focus. It's more like a gotcha taken as an easy target by people who don't want the system to exist.