ᐅ Filling the corner around the window – using rigid foam boards such as extruded polystyrene (XPS) or similar materials

Hello colleagues,
Our house will be plastered next week, and by then, three corners on the house need to be filled.
The window frame is made of aluminum, the roller shutter boxes are plastic, and above them, insulation made of styrofoam is installed.
Gluing Styrodur (extruded polystyrene) might work, but it cannot be adhered directly to aluminum because of too much movement. The only possible solution would be to attach a chipboard panel and then glue or screw the desired corner onto it. The question is, does anyone here have experience with how these corners may be filled?
Are there perhaps any technical drawings showing the correct method for this? I would appreciate your suggestions.

Photos of the window are attached. In one photo, the corners have already been filled with Styrodur but had to be removed due to the movement around the aluminum. The second photo shows the corner that needs to be filled.

Thank you in advance for your advice on this window issue.

These are thermally critical corners. The responsible trade (window installer, energy consultant, construction supervisor) should have considered this in advance, shouldn’t they?

From what I know, matching profiles made of the same material (aluminum / plastic) are installed on the exterior (from window corner to window corner) to create a visually appealing transition. These are usually glued or riveted, sometimes screwed. Presumably, the cavities formed are then insulated (sprayed foam insulation?).

Ahem... What does the window maker/metalworker say? That should primarily be their original task. And what is the architect's opinion?
Could this not be insulated with mineral wool or something similar? Then rivet/screw on a large angled sheet metal? The responsible parties mentioned above should be able to specify and explain this to you.

What does the person who designed this corner say?

The architect says it would be better to bridge the gap to the aluminum with an OSB board first and then glue the Styrodur board on top to avoid any movement between the materials. Since it is not possible to properly install the OSB board in the given situation, gluing remains the only option, but with a gap from the aluminum. Does anyone know if it would be possible to screw the OSB board to the shutter boxes in case of necessity?

So, I just spoke with the window manufacturer. Screws can be inserted up to 1 cm (0.4 inches) from the outside or inside.