Roof covering and solar technician selection - Decision?

A completely different question. If everything is installed and the commissioning by the electricity provider is still pending, can I still use my own electricity in the house? I’m mainly concerned about the heat-up program of the underfloor heating... (this is about a new building, after all) It would certainly be good if the air-water heat pump runs directly with photovoltaic power (even if in November / December not much will probably come from the roof).

Oh dear, you’re opening a bigger can of worms than you might think. ;)
There are often major misunderstandings on this topic among electricians and providers.
Especially regarding feed-in tariffs, this has been a recurring issue.
To my knowledge, the provider is not required for the commissioning of the photovoltaic system (but many providers see it differently and these lead to very exhausting discussions).
Some even want money for it...
It’s different with your house connection.

Can someone explain to me how this can be if this law exists? It seems that this law has been around for a while, so new TVs and espresso machines should belong to it as well?

You wrote above yourself that these are older devices.
Maybe the devices are actually not off/in standby but simply on.
And another question is how you are measuring, because some "meters" do not measure the active power correctly.

if I add it all up, then the consumption becomes clear to me.

No, the total for you so far is 2 kWh in standby per day. So you need 5 times as many high power-consuming devices. You are still far from 10 kWh per day.

It's about the two new devices, that's clear! The OLED and the portafilter. Please explain to me how to put a TV into standby other than turning it off until the red sweet light comes on. A fully automatic machine also has only the one power button. What do you understand by standby? Example printer: it goes into standby by itself, I don't have to press anything. It has a power button on the side but I don't press it to make it consume 0. So I also don't press a switch on the TV, do you? And the old Samsung TV that is at least 10 years old, it can do that too? I turn it off and it consumes 0.x.

No, the total for you is currently 2 kWh in standby per day. So you need 5 times as many high-power consumption devices. You are still far from 10 kWh per day.

No, it is 4 kWh all together. I now also need 3 with all the other devices that are still there. Delta: 3 kWh that I am still looking for.

So what I’m supposed to make of your comments now, I don’t know either.

I’ll leave that up to you.

And another question is also how you measure, because some "meters" do not measure the real power correctly.

exactly, most €10 energy monitors can’t do that…

The OLED and the portafilter.

The OLED certainly does not need 40W in standby. As mentioned, it can consume that much after being switched off or sometimes intermittently to refresh the OLEDs, but not all the time. I cannot say what is going on with the portafilter. Ask the manufacturer or contact consumer protection. But please check your measurement method beforehand. ;)