Did research online, found a matching story at appliance parts pros.
Tested the sensor, which was fine.
Ordered a new control board and also a new sensor, replaced both, and voila works like a charm.
I appreciate that this is a genuine Bosch part, 100% match.
It is a build-in oven, so it took some work to pull it out and remove the microwave fixed to the top of the oven to reach the control board. But it was not difficult.
I recommend taking lots of pictures before taking things apart, so that you have a reference to look at when putting it back together. This is especially important with connectors to the control board. If you have several identical connectors, mark them with a sharpie before taking the picture.
It was very satisfying fixing this myself, definitely better than waiting for a repair guy to show up in some inconvenient long window.