Room thermostat with rotary knob from Busch Jäger

I thought that the thermostats at the different levels close the valve at the corresponding temperature in the room. As in the uploaded picture...

yes, something like that... as already said at the beginning, these are more like estimates. +/-1-2° is not uncommon.

If you ask around a bit, many even recommend completely deactivating the room controllers.

Then the temperature would be the same throughout the entire house?

Google "Hydraulischer Abgleich"

A good tip. Had you already done that?

Yes, but it is still not completely clear to me. I just don’t understand the connection between room thermostats with the rotary knob with 6 levels, settings on the tower for the desired temperature, and supply temperature and outside temperature :-)

Then the entire house would have the same temperature?

No, exactly that is the wrong way of thinking.
As I said, please google hydraulic balancing and efficiency/operating point of a heat pump.

It is a misconception that the heat pump uses more electricity if it runs ALL the time. It is effective when the heat pump runs often and for long periods at a good operating point.
--> That is why hydraulic balancing is done.