Here's a completely parametric air vent adapter I made a couple of years ago.

I used to live in a double brick apartment block (cinder blocks for interior walls). As I was renting, I couldn't install a permanent air con and as I was on the top floor and the place had an iron roof, it was basically an oven in summer (Who am I kidding an Aussie summer turns just about any place into an oven)

So I procured a portable air con. Issue was that the thickness of the cinder blocks meant that the window sills got in the way of putting the vent in the window correctly.

Few hours designing and several more working out the math and I had this... then i moved out so never actually ended up making it.

I recently saw someone post something similar and it reminded me of this, so here ya go have 1 that you can make any shape you want. It has been designed to ensure no restriction of air flow but that being said don't go setting up a 10cm pipe to got through a 1 cm gap (don't think that it would even fit on a printer bed)

The parameters are as follows:
Input Pipes Diameter
How much lip is required to connect the input pipe to the adapter
How big a gap you want between the window frame and the window itself (ie the width of your plank of wood minus whatever's going to fit inside the frame)
mow mush lip is required for screws to attach to plank of wood.
how much you need to offset the pip to clear any obstacle like window sills ect (recommend playing with this a bit, generally you want one side to line up with the start of the window opening so you guarantee it wont hit anything)
how big a transition zone is required, this will determine how noisy it is but is restricted by how high you can print.
how far out do we need to go from the window before we can start the transition to the pipe
finally how thick we want the walls to be

It will take all these to work out how wide the slot in the wood can be to still allow enough room for screws and then extrapolate from this and the desired pipe diameter how long the slot will need to be to accommodate the volume of air that the pipe can pass.

we do this by splitting a circle in half and inserting a rectangle of the difference between the 2 openings in between

area of rectangle = area of cross section of pipe - the area of the biggest circle we can fit in the window gap mins the screw lip either side.

Though the code doesn't actually use a cube, it just draws 2 cylinders and hulls them so we get nice seems no matter what wacky numbers we end up with. then the opening is made by subtracting the thickness from all dimensions (designed to go inside pipe so cant go larger than diameter)

Anyway, have fun. experiment with the variables to get your desired result