Understanding window inner size vs physical resolution
When you ask what is my screen size there are really two answers. The physical resolution is the total pixel grid of your monitor. The window inner size is the smaller rectangle your web page is allowed to paint in, after the browser chrome and scrollbars are subtracted. Layout bugs almost always relate to the inner size, so that is the number to trust when debugging.
What is device pixel ratio (DPR)?
Device pixel ratio ties CSS pixels to physical pixels. On a standard display the ratio is 1. On a high density screen it is often 2 or 3, meaning each CSS pixel is drawn using several physical pixels. Multiply your inner size by the DPR and you get the physical pixels shown in the report, which is what you size raster images against.
Available screen workspace and colour depth metrics
Available screen size is the desktop area minus fixed system bars like a taskbar or dock, which is why it can be a little smaller than the full resolution. Colour depth reports the bits per pixel your display advertises, usually 24, describing how many distinct colours it can show.
Exporting diagnostic reports for bug tracking
Use Copy report or Download JSON to capture every value at once, including the user agent and a timestamp. Dropping that into a ticket gives whoever picks it up the exact display context, which removes a whole round of it works on my machine back and forth.