Experiences with alternative route rights / judgments

You are already getting upset about something that is rather unlikely and neither obvious nor plausible.

Yes, it is very likely that the WBG will approach you.
And it will be so that you have to give up the right of way.

But where does it say, please, who says that they want to drive along the entire south side? Or over the yard and not directly using the yellow option? Why should they inconveniently take two extra curves if they can directly use the already existing driveway?
What do you base your assumption on, which you take as given here?

It can’t be that the entire yard area is taken away and parking spaces plus flowerbed etc.

Who says that?

But that one would also have to allow access through one’s own property, I don’t see,

No one wants anything yet.

But then driving over the entire yard area (orange) to get to the underground garage entrance and parking spaces, that’s what we are annoyed about.

Why should they? No one has talked to you yet.

Private path and yard area are one parcel of land.

So what? That doesn’t matter at all. An easement of right of way will be implemented directly. At least, that’s how it is supposed to be.

My primary concern is that the existing direct path to the existing driveway onto the WBG property is to be eliminated and that instead our entire yard area is to be used.

Who says that? Nothing has happened yet, as you say.

Path is path and yard is yard

Exactly.

If WBG plans an underground garage and some parking spaces, then they will also pave a yard so that they can cruise within their property. That is the most obvious. So just stay calm.

A different perspective: Why or since when does a property even exist without access?

According to § 918 para. 1 of the Building Code, a right of way is not to be tolerated by the neighbors if the previous connection of the property to the public road is abolished by an arbitrary action of the owner (in practice usually the development of the previous private path or division into several properties without sufficient and secured access).

Perhaps there is a starting point here?

I have meanwhile read multiple confirmations supporting my view that [Notwegerecht] is primarily a right of passage on foot without an automatic right to drive, and that no right to install utilities follows from it. On the website of the law firm Kotz (Siegen), information is provided regarding OLG Karlsruhe, Case No. 6 U 240/93, Haufe mentions BGH, judgment of 26.1.2018, V ZR 47/17 (concerning the right to install utilities) – specifically regarding my view that [Notwegerecht] is not intended to create an access for development in order to change the use to a building plot, I have found no statements so far. As a result, I therefore maintain the opinion that this intended enhancement (comparable to what would be called an "improvement" in social law) is not an "emergency."

Who says that?

The planned development has apparently only recently become known:

On the WBG drafts it can now be seen that an underground garage access as well as additional above-ground parking spaces are planned (orange marking). However, these cannot be reached directly (green arrows to the yellow existing access) but only via the courtyard area (orange arrows).

Again. Lawyer. This is about more than Viessmann vs. Buderus.

I currently consider that premature and accordingly a waste of money. Nothing has happened yet.

Not me. The claimant is a housing construction company. Professionals. This is about a lot of money and every millimeter. And undoing facts created at the construction site... well, how often do violations against fines get through, and then it has become a fact. Every day where something can still be stopped and prevented is precious. If necessary, the entire building permit could still be overturned. That would be the best.

The planned development has apparently only recently become known:

however, the planned development has nothing to do with the fact that the property is accessed over a distance of roughly 15 meters or via 2 access roads or through a courtyard that belongs to 3 houses. Just because the development includes several parking spaces, they do not have to be accessed from the outside (private courtyard, private road), but can be accessed via a property area.

The second possibility seems to have arisen from "interpretation through fear" and in my opinion is absolutely far-fetched.

It doesn’t matter at all whether it’s a single-family house or a multi-family house: a property rarely has more than one driveway or one larger than 6 meters. Yes, that can happen if the circumstances are right, but that is definitely not the case here, if you think about it.