How does our heating work in the new rental apartment?

Then you just don’t have a central control. Not every house or apartment has to have one. I mean, when you visit an apartment, you already think about what the technology offers or which technical features are not available.

During the inspection, we didn't give it any thought. But the question is why the radiator gets very hot when you turn it to 0.5 and then at some point is no longer that hot. Is that normal with this type of heating? That's why the question was whether it is practically just "on" and "off"...

But the question is why the radiator already gets very hot when you turn it to 0.5 and then at some point it is no longer so hot.

Every thermostat on the radiator only knows open and closed. At 1 it is fully open (if it is cold enough in the apartment) as well as at 5. But at 1 it closes again at the appropriate temperature (e.g. 18 degrees). At 5 only at 26 degrees.

Is that normal for this type of heating? That was the question whether it practically is only "open" and "closed"..

It is like that with all radiators. Open and closed – there is nothing in between.

But the question is why the radiator already becomes very hot when you turn it to 0.5

because it is too cold in the apartment and it has to power up.

and then at some point it is not that hot anymore.

because the temperature in the apartment becomes more comfortable and then the "not that hot anymore" is sufficient.

Ah, ok. In your post you write 1 = 18 degrees. In the old apartment, the installer told me: 1 = 12, 2 = 16, 3 = 20, etc., with the corresponding intermediate steps. What are the values?

One more question: Does it make sense to heat to 20 degrees for 30-60 minutes every 2-3 hours during the day and then maintain this temperature continuously in the evening, or rather keep a constant temperature? Also considering consumption?

Thanks for the feedback in advance.

In your post you write 1 = 18 degrees. In the old apartment the installer told me: 1 = 12, 2 = 16, 3 = 20 etc. with the corresponding intermediate steps. What are the values?

My values were made up.
Common is:

[*]Level 1: approx. 12 °C
[*]Level 2: approx. 16 °C
[*]Level 3: approx. 20 °C
[*]Level 4: approx. 24 °C
[*]Level 5: approx. 28 °C