The roller shutter box is not flush with the wall - possibly a planning error? Any ideas?

Hm yes, monolithic and installation position rather far outwards. I doubt that such deep boxes would have been available for selection at all. On the other hand, this should be known/clear to the general contractor, unless he is producing a monolithic masonry for the first time.

The usual dilemma: One did not point it out, the other did not ask.

Maybe another builder with monolithic construction has some experience to share.

Edit: Just checked, we have Konax boxes, which seem to go up to 300mm. So it is possible after all ... They also offer doubling up from the system (additional base plaster boards).

Definitely double it, how many blinds are there? I had to double it by 3 cm myself :/ Do you have an XPS cutter? Otherwise, ask around, those things only cost about 100€ With a can of adhesive foam and a few m2 of XPS, you might need about 30 minutes per window and it costs maybe 40€ in materials. I took about 3 hours for 20 linear meters of windows. Annoying work but better than such a protrusion

Definitely double up, how many raffstores are there? I also had to double up 3 cm :/ Do you have an XPS cutter? Otherwise, ask around, those things only cost around 100€ With a can of adhesive foam and a few m2 of XPS, you might need about 30 minutes per window and it costs about 40€ in materials. I needed about 3 hours for 20 linear meters of windows. Annoying work but better than such a protrusion

There are 8 of them, partly 3m wide. The plasterer wants to screw it if he does it. Are you sure that bonding works with 20cm thickness and that width?

There are 8 pieces, partially 3m wide.
The plasterer wants to screw them if he does it. Are you sure that gluing works with 20cm thickness and that width?

Is the armor made of plastic?
Gluing should work. But of course, 1 plate dowel per 50cm would be safer. They are called facade dowels and could then be anchored in the lintel. However, if you prime the lintel and use proper adhesive foam, nothing should happen.

It's really annoying when such details turn out so differently than expected. In any case, you need a solution that brings you lasting peace with the situation. Will you also have curtains / drapes in front of the windows? If the recess is suitable for it, you can visually create flush surfaces with a curtain. The rod then runs exactly in the recess. A bug would become a feature. From the pictures, I can't judge that 100%, but maybe it's worth considering for you.

If you are going to use dowels, then into the reveal, not into the box. Just for the sake of completeness ;-) I don’t think the idea of doing it yourself is so bad. The plaster will make it look nice anyway. You just have to create the approximate level (or 1-2cm less).