There is more to it than that, though, as many of the existing DTHs already do have a child device for each button, but they don’t work in the new app.
There are multiple threads discussing this issue in the forum already, so I’d rather not go into the details here.
Here is just one example of one DTH that was eventually updated to work.
However, I have seen at least two different methods for updating these, and again, nothing official to explain what updates are required. Just lots of community members trying to figure it out.