IIRC, win8 was the last windows to have thick graphical window borders, and that was after they got rid of the texture/aero look from vista/7, so at that point you at least had something graphical to grab onto which (mostly?) matched where the cursor was. Then in win10 onwards they shrunk the border down to one pixel with the zone around it where you can click off the window but still affect it.

On the back of my mind I think part of this was the move to fit scaling to large resolution monitors (i.e. 4k+) work better, as a graphical border of a fixed pixel width will shrink proportionally compared to a border that is as thin as it can be. For a while I've felt that it's a missed opportunity on high res displays to not use more detailed art for window chrome as pixel wide will only get smaller and more difficult to distinguish, such as the minimize/maximize/close icons which remain pixel wide line art even at big scaling.