PNG is a raster image format, like JPG but PNG is popular because it allows transparency and doesn't have JPG compression noise except in case the image was originally JPG. Inkscape has very limited raster image editing possibilities. In Inkscape you cannot select a part of a single raster image for edits, as you have already noticed.
If you still want to make raster image edits in Inkscape, you can as a workaround insert another raster image on the top your photo, one which is cropped or masked to cover just the area which needs something new. Apply your edits to the inserted image or insert a ready to use image which doesn't need any more edits.
To hide the unwanted areas of the inserted image you can draw a clipping path to it in Inkscape if you want, but generally it's easier to crop the image and make the unwanted areas transparent in a raster image editor like GIMP or Photoshop. It's easier in Inkscape only if the needed clipping path happens to be extremely complex or it's already available in Inkscape because it's also used as a part of the artwork.
This is in Inkscape, but I have prepared (=clipped from your photo, colorized and made the unwanted parts transparent) in GIMP a new brownish frame to your window. It has everything else transparent except the wooden frame. It's exported from GIMP as a PNG file to keep the transparent areas and imported to Inkscape. Copy and paste directly between the programs does not keep the transparency. A copy of the new frame is shown in the left just below the Objects panel.
It's much easier to do the whole job in GIMP or Photoshop. In Inkscape one makes easier parts which must be vectors - like construction and material explanations or planned things which can look drawings.