Separate awarding of windows and shutters - GU resists!

The keyword warranty has already been mentioned. It opens all doors and gates for the general contractor, especially with windows. If the screed warps, he can easily blame the windows. Benefit and stress must be critically assessed here.

With today's wall thicknesses, it is no problem to install an electric roller shutter in front of the windows that can be plastered over. The window installer must fit a correspondingly large strip at that point, and additional insulation will be added from the inside.
Basically, I also don't think it is particularly wise to separate a large trade from a general contractor contract in the middle of the process. Delivery times for windows were quite a lottery this summer, and you quickly run into problems if your window installer causes delays.

With today's wall thicknesses, it is no problem to install an electric roller shutter in front of the windows that can be plastered over. The window installer simply has to fit a sufficiently large strip at that point; from the inside, additional insulation is applied.

Perhaps for windows with sills. For floor-to-ceiling windows, I don't think so. You would have to recess the windows all the way back to the interior wall so that it is flush on the outside. And then, inside, above the window, the extension is directly on the interior wall. It might be possible to plaster over it with a bonding bridge, but cracking is definitely to be expected there. So it will never look nice, and I definitely think it will be very labor-intensive.

Works also with floor-to-ceiling windows. The insulation on the inside was then plastered over with reinforcing mesh. Presumably the same on the outside when the time comes. I cannot say anything about crack formation yet, it is still too early for that. Currently, however, nothing can be seen from the inside anymore.

And what wall thickness do you have?

You could take the windows including the roller shutter box and then install motorized roller shutters separately. However, the electrical connection must be prepared from the inside and the window manufacturer must already take the guide rails into account (afaik). Whether he will go along with that ... probably not. Why should he.