Recommendations for sealing a casement window for a portable air conditioner

[Quooth]

I have a portable air con unit which I've had for years and it's getting some use this year. I've never bothered with sealing it but it's obviously not as efficient with gaps.
I wonder whether anyone has any recommendations for sealing a casement window. I can sew but not good at DIY.

https://amzn.eu/d/00NTKzll

Bought this earlier in the week. Instructions are TRIPE but once figured out it works fine.

That's the idea! It just looks like a piece of fabric.
How are you finding it?
I realised that I was letting hot air right back in the open window.

Just be aware when using a single hose AC unit, it relies on drawing the same volume of air into the room, as it blows out of the hose.

So sometimes it's better to have a window in shade slightly open, than forcing it to suck air from the loft or floor below etc

Well, it's ace now it's up! But trying to read the instructions in size 5 font at 30 degrees nearly sent me loopy.

In the end I had to photograph them, feed them into Claude and ask him what the hell to do with it. Turns out it was super easy once you understand what it is!

Basically you get a roll of sticky backed velcro. Cut it to the size of each edge of your window frame and the opening part, so you essentially have two velcro rectangles round the window. Then the flappy fabric bit attaches to them, with a zippered line down the middle, and you stick your a/c hose through the gap and zip it tight.

@LividSun I already have velcro around the window. I made mesh pieces to fix up to keep insects and cats out ( dormer).
If it's only fabric I can just cut a piece to size, make a slot in the middle and sew velcro on and use instead of the mesh.
For tonight I've fashioned a big piece of cardboard.