If you’re somehow measuring your window’s size in physical pixels, then yep, welcome to the modern world, where physical pixels are no longer what people use to define their window sizes.
The Windows high-DPI handling has always been a total car-crash, and unlike OSX where it abstracts the physical dimensions from apps, on Windows we have to add our own scaling to correct for the monitor settings. But it’s done deliberately to stop your app looking ridiculous on highly scaled displays, and you should embrace it, not question it!