Air heat pump or use gas and solar?

You are right. In principle, I am also against an external device. But I find this option so innovative and interesting that I can imagine the compromise because - at least as I read it - different price development scenarios for gas and electricity can be well represented. It is also possible to do without mounted flat plate collectors and expensive tube collectors.

Another alternative I am considering is to have flat plate collectors placed in the garden. There they don't bother anyone.

Are there actually any additional costs for a gas connection besides what the supplier charges? They want €1190. Relevant information suggests that a gas connection is supposed to cost somewhere between €1500 and €250. What other costs come in addition to the house connection by the supplier that you wouldn't have with a brine heat pump?

The acceptance of the fireplace by the chimney sweep is a one-time cost of just over 100,- End. Nothing more.

The excavation of the foundation pit and its subsequent backfilling, unless this is already included in the 1190€ (which I actually do not assume)

That is included. 1190,- is already expensive. Here it was 750,- with trench max. 15 m. Above that, surcharge.

I had briefly considered a hybrid heating system. There are also experience reports about an increasing electricity consumption and maintenance costs beyond €400.

So you really have to buy gas/solar even if in the end it is equally expensive or more expensive than the heat pump solution. Sad. It will certainly be quite a bit more expensive because of the tube collectors but angled flat collectors don’t work.