It takes a long time for hot water to come

Yes, sparing with water, electricity consumption high 5

Circulation should definitely be done in the new building. But that ship has probably sailed...

It is an old building. And no, the electricity costs are extremely low. We need 600 kwh per year for hot water with the instantaneous water heater, and the electricity for the pressure boosting pump, which runs on three-phase current, is already included! When showering at 41°, it only requires 5 kW. Without a circulation pump, long pipes from the basement, and heat loss due to constantly keeping hot water in a storage tank. So where else could it be cheaper?

Circulation runs very precisely and time-controlled, furthermore it is specially insulated. The heat loss is therefore very manageable.

Without an instantaneous water heater, exactly. I have the same hot water costs in a 4-person household with daily showers for everyone and a weekly bath. With circulation and all the bells and whistles... of course the conditions are different but that's how it is...

So where else would it be cheaper?

With a heat pump, you have about four times lower electricity costs.
Now you can offset the additional installation costs; in your case, the instantaneous water heater might actually be cheaper, I can't assess that.
In general, considering average consumption as well as installation, maintenance, and upkeep costs, an instantaneous water heater is the most expensive option you can choose.