macOS Mojave 10.14.4 Beta 18E194d
MacBook Pro (15-inch, 2018)
Processor 2.9 GHz Intel Core i9
Memory 32 GB 2.4 GHz DDR4
Graphics Radeon Pro 560X 4 GB, Intel UHD Graphics 630 1.5 GB
UHD 8K (7680x4320p60) Quicktime X (10.5) Playback.
All ProRes: No
H.264: 8K not supported
H.265 8-bit: Davinci Resolve hangs
H.265 10-bit: Too long to render in DaVinci Resolve
8K and a Beta release of macOS clearly do not mix. The good news is that the AMD WX9100 is fully utilized during 4K HEVC H.265 rendering within Davinci Resolve 15.2.4.
Quicktime X on the other hand shows neither CPU nor GPU using while exporting the HEVC, leading to the idea that some hyper efficient hardware acceleration is implemented well between macOS and the Intel chip.