I found a slightly better fix, if you go to
Control Panel (make sure in the top right view by is set to large/small icons) → Mouse → Pointers → Select ‘Windows Default (system scheme)’ → Scroll down to ‘Precision Select’ → Browse… → Select ‘cross_r.cur’ → Open → Apply
The issue is with the precision select cursor (particularly with the cursors that invert the colors of what is behind them); when UE is in focus, windows renders UE viewport content over the inverted cursor instead of the other way around. There are other cross cursors as well, such as ‘cross_l’ or ‘cross_rm’ but I haven’t tested those so your mileage will vary.