I've been asking myself that for a long time now, every hour of every day.
the ultra version doesn't work at all

What height can this overcome? We have 4cm as the highest door threshold. Or can anyone recommend a robot hoover including wet pick-up?

According to Roborock EU, it will not be available in the EU until around May.... But we do not know

You could pre-order it at Media Markt / Saturn Germany with delivery in May.