Difference in purchase cost between gas pump or heat pump

In addition, electricity is supposed to become cheaper by reducing the Renewable Energy Act surcharge. That does not exclude the fact that electricity tariffs with fossil fuels become more expensive, as CO2 charges will apply there (either directly shown in the electricity price or included in the producer price)

That is clear. Only the Renewable Energy Act surcharge is included in every kWh of electricity, regardless of "where" the electricity comes from. And thus coal power also becomes cheaper – and that is nonsense

Are there, besides the underfloor heating with low supply temperature, any other points to consider when building a single-family house in 2020 with a planned gas heating system, so that if necessary, one could switch from the gas heating to a heat pump in a few years?

- Well-insulated building envelope - Controlled residential ventilation with heat recovery - Plan the technical room accordingly (space for heat pump and space for an outdoor installation)

- Plan the technical room accordingly (space for the heat pump and space for an outdoor installation)

meant a split heat pump, so plan the technical room there in the basement, where there would be space for the heat pump outside in the garden. Okay thanks!

That is clear. Only the Renewable Energy Sources Act surcharge is included in every kWh of electricity, regardless of "where" the electricity comes from. And thus coal power also becomes cheaper - and that is nonsense

The actual electricity mix at your socket is unknown. How should price control be implemented on this basis?
The Renewable Energy Sources Act surcharge is the same for every kWh, whether the electricity at the socket is actually 100% coal, nuclear, or renewable. Regardless of whether an electricity tariff with a different electricity mix was concluded. Therefore, there is only "up for all" and "down for all".
The Renewable Energy Sources Act surcharge is used to finance renewable energy sources. You pay it regardless of the electricity mix.
This does not make coal power cheaper; on the contrary, the cost portion for generating electricity is actually higher for coal power because the power plant operator who emits CO2 has to pay for these emissions.

meant a split heat pump, so plan the technical room down in the basement, where there would be space for the heat pump outside in the garden.
Okay thanks!

Yes, the structural requirement to retrofit a heat pump is needed. Usually split systems, i.e., refrigerant lines and electricity are required to the location of the outdoor unit. The installation location should also be suitable, e.g., not on your own terrace or close to the neighbor.
A heat pump with indoor installation would also be possible of course, but it requires enough space in the room and two relatively large outlets for supply/extract air.

I like to say it again and again, the so-called Geisha air-to-water heat pump costs 2500 euros as a monoblock. No gas line, no chimney, and an annual performance factor of 4 is quite possible. Installation can also be done yourself with some skill. There are countless examples.

I like to say it again and again, the so-called Geisha air-water heat pump costs 2500 euros as a monoblock. No gas line, no chimney, and an annual performance factor of 4 is definitely possible. Installation can also be done by yourself with a bit of skill. There are countless examples.

+ no maintenance, no chimney sweep, and the photovoltaic electricity can be used by yourself. In my opinion, gas no longer makes any sense at all.