The mono conversion is very strong. I might have cropped along the top horizontal taking the three top rectangles windows out of the shot and using the horizontal black window frame as a natural frame / border on the top.
Similarly I would have done a little crop off the bottom horizontal, making sure the diagonal window frame shadow leads in from the bottom right hand corner (therefore acting as a natural lead in line taking our eye into the shot and onto the man).
The mans jacket / backpack is very silhouetted / black. I don’t know if you could bring out some detail there (dodge /burn tool), but I think it works fine as deep blacks, but some people might want to see some detail
I would have quite liked to see an aeroplane in the shot too, maybe on the far runway or even in the sky as this then “tells the story” and puts some context on the image. If not an aeroplane then maybe there was one of those orange wind direction thingies to the left or right. At the moment it is a man looking out of a big window, we have nothing in the frame to tell us why he is there.
It is a strong shot though and I am only suggesting minor changes as you wanted a critique
Have a nice day