That image to me looks like a cold bridge/damp wick - whereby a small portion of the outside masonry is visible beyond the DPC break (older propery jamb detail) after the window was positioned and fixed.
This is often an issue with window fitters preferring not to shove the window far enough back into the room. Rather, they position the window (wrongly) so that it is easir for them to fix but leave a small amount of external masonry visible beyond the edge of the window jamb.
A small amount of the external lintel is visible here along with condensation dripping off the external lintel.
I took this photo to show the window fitting boss.