Regarding the missing pinch gesture, I now did two additional things:
- Manually resetting the device, which puts the device to fw 4.32.x. But after upgrading to the latest fw version, there's still no pinch gesture.

- I contacted the Kobo customer support via chat. After answeing a few questions and telling her that even the manual reset didn't help, she silently left the chat.

So now I'm stuck.I also couldn't really figure out how to get Kobo a bug reported. I suspect that the customer support person did not pass on the problem.