Dragging a window to one of the workspace thumbnails in the workspaces bar in GNOME Shell 40 does not show a drag target affordance highlight border
When dragging a window from GNOME Shell 40's new overview to one of the tiny workspace rectangles above the current workspace, the mouse cursor changes but there is no clear indication of which workspace the window is successfully being dragged into; there would need to be some highlight* around the receiving workspace thumbnail, to visually communicate its affordance as a drag target and that it is indeed the drag target, not the other workspace on the left or right of it.
Otherwise it's not super easy to see clearly when you have the currently-being-dragged window overlaid transparently with the mouse cursor.
*: I would suggest a white highlight/border, to complement the current blue highlight/border around the current active workspace