Terraced house without real division: disadvantages?

Topics such as garden design, terrace, installation of photovoltaic systems and similar should not be affected by the WEG?

That should be stated in the contract. Also whether you are allowed to install awnings or terrace roofs. In the case of apartment buildings, the appearance of the balconies may sometimes be regulated. Basically, the development plan applies. Possibly also a design framework. It can and does happen that a uniform appearance is required. But this can also be the case with a real division. Impossible things or things one could not live with are not demanded.

Topics like garden design, terrace, installation of photovoltaic systems and similar should not be affected by the WEG?

(of course all within the usual framework of neighbor law)

That should be regulated by exactly what is individually owned property and what is common property. We basically have a horizontal condominium with a garden. Roof, garages (courtyard), house connection room (a power supply line for 5 houses), all common property.

We now want a wallbox at our garage and balcony power plants next to our roof window. There are quite a few meters to be done for us, we obviously cannot just do it as we please. It's annoying.