How to best insulate above and below a window

[HumanAstronomer3194]

I had previously posted https://www.diynot.com/diy/threads/window-frame-falling-to-one-side.649352 about a window falling down. Now I want to insulate above the window and I'm wondering what is the best way to do this. As I understand if I do this incorrectly I can cause moisture to get trapped here.

Do I just stuff some rockwool insulation up there then put some vapor barrier before finally closing it off with insulation tape? Bearing in mind this is a flat roof and these are the joist running on top. Also the gap between the window and plasterboard was covered with small bit of wood trim.

Before the screws were installed.

And for the below the window do I just fill this space with insulation boards?

With the window cill removed and looking down

 

[Wayners]

I can't work out what I'm looking at.
Looks like the roof has a big hole in so does rain get in?

 

[HumanAstronomer3194]

I've updated some of the photos.
There was a gap at the top of the window frame that has now been fixed. Below the window there are the yellow panels that can be removed exposing the timber and felt.

 

[Wayners]

You can shove glass fiber in then cap off with a vent.
That way it's not sealed off but insulated.

If you use foam insulation board you seal off with mastic but fit a vent inside.

I'd go with glass fiber.
You may get better advice here.