A window over the sink that opens is wonderful. It looks like you can lock and unlock it easily without standing on a step stool.

If you really think you'll like being able to open the window, keep it. Solve the light problem with correct lighting in the kitchen. If the kitchen faces north or there are a lot of trees outside it's going to be dark without good lighting. All I see right now is one can light. Were you planning on adding fixtures as part of this project? I suggest you read this for more information on kitchen lighting:

https://languageoflight.blog/2023/01/11/dont-do-this-kitchens/

To brighten a kitchen requires really good lighting since often the time you spend in there is when the sun is not shining Not sure wht was there before but wider would have been a better choice but now get better light . I like LED 4000K in kitchens you can go to 3500K but IMO anything lower gives the whole space a yellow glow. You need many pot lights , some under cabneyt lightis and if you have an island some pendants to light it .

Can you install more windows in that area or are there upper cabinets?

There will be upper cabinets. Wish we could have done more windows but that was too extensive

I would keep what you have , extra 2” not that significant plus you can open this.

I say go for a fixed window. Just put it in as an added window. Because you're not getting a refund on the one you've already installed. . .And you need a good task lighting plan for your work zones. Plus, I hope all your lowers are wide drawer units. Single bowl sink.

Can you do a dry wall return, which then does not need trim.

There is something pinched and strange looking about such a narrow window in a kitchen. It looks more like a window you might find in a bathroom, a stairwell, or a tiny urban studio apartment. When the window is hemmed in by upper cabinets, it will look and feel even more claustrophobic. You’ll be standing at the sink and those uppers will be close to your face and constantly in your view.

There will never be a less expensive time to add a larger or second window than now. Get scratch ’n dent, used, or low-end appliances if necessary to make budget room. Heck get the least expensive countertops. All that can be very easily changed later; this weird window cannot.

How did it turn out?