Window replacement, reveal insulation, and windowsill

Hello, I had a new kitchen window (triple glazing ug) installed in my RH built in 1986 and want to insulate the reveal.

At first, I wanted to insulate with multipor reveal boards but I am not sure how to do that with the window sill. Because these boards are 2 cm thin and very brittle. If the new window sill is to be made of Dekton/ glass or something heavier, then I fear that the reveal board will give way due to the weight.

Is insulation actually installed under the window sill and if so with what? Can you use a Wedi board?

What alternative possibilities or materials are there to multipor? If I stay within the system, it will be a bit expensive for one window and I would have to throw away a lot of material afterwards.

Attached is a photo of the window.
To the left and right of the window sill area is the old foam.
The new window was installed as follows.
Inside wind barrier, then Soudal MF 167 foam, compressible tape. The window was of course also screwed in.

According to the construction documents, the wall structure is as follows:
11.5 cm VMZ, 4 cm air gap, 6 cm core insulation, 17.5 cm rear masonry KSL.

You can practically use anything. From Styrofoam to EPS, XPS, Resol, PUR, etc.

Under the windowsill, however, it doesn't look like there is any space left for anything if a 20mm windowsill is supposed to be installed there.

Thank you. If I use XPS (Wedi or Ultrament) everywhere, what should the panels be glued with? Ultrament recommends their hybrid adhesive, others say best fully covered with tile adhesive... How are the corners/joints sealed? In the reveal bottom right and left, there is still the old foam and the cutout is not straight but slightly bent inward/concave. Since the insulation panels and the windowsill on the narrow outer sides should not be flush with the reveal (5mm into the wall), I have a gap. The attached wind barrier also has a gap in these corners. After scraping out the old foam, what can I use to fill this gap?

If I use XPS (Wedi or Ultrament) everywhere, what should I use to glue the panels?

Whatever you want. PU foam, tile adhesive, lightweight masonry mortar, construction adhesive, Jackodur perimeter adhesive, etc. You can certainly find about 30 different products.

I would simply glue the (whichever) panels. Either down to the bottom and then slide in the windowsill or leave space for the windowsill and set it in the reveal. Plaster and done. If anything is open, you can use, for example, hybrid sealant from Ottoseal (M360). All of course DIY and not with any system approvals, but it works.

Ok understood. I forgot to mention that the distance between the bottom edge of the window hinge (bottom left) and the parapet is about 6cm. Can I manage with a 2cm windowsill and a 2cm insulation board without adhesive, or should I rather use a thinner insulation board?

Can I manage with a 2cm windowsill and a 2cm insulation board without adhesive, or should I rather use a thinner insulation board?

Sure, that can work. Whether it looks nice, you have to decide.