I have this window in the wall I’m putting pegboard up on. Because of the holes, pegboard does let some air and light in, but I decided to cut out the window opening so that I could operate it.

You could carefully measure the opening, cut a big section out of your pegboard panel, and then install it. But, because this opening would make my pegboard panel into a giant “C” shape, it would make installing it by myself excessively difficult. (Also, you have to measure and cut very accurately.)

I found it much easier to just install the full panel and then cut out the opening. I’m using a trim router with a following bit. After I cut out along the top, I hung it up with wire so that the panel I was cutting out wouldn’t fall down later on.

And then I cut out the other two sides. The downside of this technique is of course the copious amounts of hardboard sawdust, which does require a shopvac to clean up.
And of course, depending upon how you install the pegboard your cutouts may go through a series of holes. But, the edges are very close to the edge of your framing members.