so I installed D2R on my iMac 5k (Radeon Pro 580) under Windows 10 via Boot Camp. Performance is pretty bad but more importantly the UI layout is broken when running in fullscreen (windowed mode is fine).
The assumed aspect ratio is simply not correct which e.g. leads to the lower UI occupying the center of the screen instead of the lower part. This also becomes evident on the screen calibration screen where the lower corners are not on the lower end of the monitor but somewhere near the center of the screen. The fullscreen resolution is 5120x2880 with 200% scaling (HiDPI display).
I have no problems wrt. this in other Blizzard games on the same system (SC1, SC2, D3).