Operate fresh water with partially very high and low buffer temperatures

Yes, exactly like that. A fresh water unit is basically just a heat exchanger. The warm water from the buffer heats the cold water from the pipe in a flow-through process.
If the water from the buffer is no longer warm enough, the fresh water unit simply heats as much as possible.
Completely harmless.

Hello.
Regarding "scaling of the heat exchanger of the fresh water unit," I have a question.
Limescale is released only from about 60 degrees Celsius. The higher the hot water temperature above 60 degrees, the more limescale is released. So the heat exchanger scales faster and loses effectiveness.

Question:
Since the supply from the buffer is very high in summer (partly over 70 degrees) and the bottom of the buffer is also very warm, the mixing valve does little to mix the supply of 70 degrees down to 65 degrees or even 60 degrees (mixer).
That means the fresh water unit receives up to 70 degrees from the buffer supply to produce 58 degrees.
Does the heat exchanger scale faster because of this (supply 70 degrees)? Or does scaling only begin in the heat exchanger when the hot water is produced (currently produced from 70 degrees to 58 degrees, although the display shows a hot water setpoint of 65 degrees)?

How can scaling of the heat exchanger be reduced in summer with high supply temperatures from the buffer?

Thank you

With the right mixture before the WT. By adding cold water.

With the right mixture before the WT. By adding cold water.

All right. For me, the "cold water" is supplied from the buffer at the very bottom. And that is also very hot in the summer. I do not have an extra cold water supply to the buffer feed for fresh water. Thank you

Yes, it makes sense and is possible without problems. Depending on the situation, you can turn off the heating including hot water preparation yourself, as long as the temperature of the hot water in the morning is still sufficient for you.

Hello again. Is it "normal" for fresh water that slight temperature fluctuations occur (you have to readjust the set shower water temperature from time to time while showering)? Several apartments draw from this single fresh water source. There is plenty of buffer volume for the fresh water (500l out of 1000l). But I have read that pressure fluctuations cause these slight variations, and are unavoidable with fresh water. When showering, it is annoying if you have to readjust the set temperature frequently. And installing a separate shower thermostat is also not the solution.

Yes, that would be the solution. With my fresh water back then, there was no such problem. But if several tapping points are needed now, 500 liters is not much either. Then there is also the question of what flow rate the fresh water has.

Yes, that would be the solution. With my fresh water system back then, there was no problem. But if several tapping points are needed now, 500 liters is not much. Also, the question of what flow rate the fresh water system has.

50-100 liters flow rate. So generously designed for the multi-family house. The 1000L buffer was practically divided so that 500L alone is reserved for the fresh water. The supply line for the underfloor heating is exactly in the middle of the buffer.