Sounds like a glitch to me. Did it perform an upgrade?
www.bhphotovideo.com
{
/System/Library/Extensions/AppleGraphicsControl.kext/Contents/MacOS/AGDCDiagnose -a | grep -E 'BR|DSC|Pixel|Bit|Color|Range|Link|Lane'
ioreg -w0 -irtk locationID
system_profiler SPHardwareDataType SPThunderboltDataType SPUSBDataType SPPCIDataType SPDisplaysDataType | sed '/Serial Number/d;/UUID/d'
} > XDR_Usb_Thunderbolt_PCI_Info.txt 2>&1
open .
You'll want to install the Boot Camp drivers (use Brigadier to fetch and install Boot Camp drivers?) to get the presets and brightness control for the XDR. Everything else should just work.
Since the 30x0 continues to support DSC, I expect it to work easily with the XDR with the right cable. For one, "The Belkin Charge and Sync Cable for Huawei VR Glass" should work.
egpu.io
If you have the 580X then it won't work. The first two XDR displays use up all four of the DisplayPort connections.
| GPU | HDMI 2.0 | DisplayPort 1.4 | DSC | 4K (HDMI or single link SST HBR2) | 5K (single link SST - HBR3 8 bpc) | 5K (dual link SST HBR2 10 bpc) | 6K (dual link SST HBR3 or single link SST HBR2 with DSC) |
| 580X | 2 | 4 | no | 6 | 4? | 2 | 2 (dual link SST) |
| W5500X | 2 | 2 | no (but it's Navi so maybe?) | 4 | 2? | 1 | 1 (maybe 2 if DSC?) |
| W5700X | 1 (shared with a DisplayPort) | 6 | yes | 6 | 6? | 3 | 3 (dual link SST or DSC?) (6 possible connections with DSC but no-one has tried more than 3?) |
| Vega II | 1 (shared with a DisplayPort) | 6 | no | 6 | 6? | 3 | 2 (dual link SST) (but people have successfully used 3) |
| Vega II Duo | 1 (The Mac Pro white paper says this is not shared) | 8 | no | 8 (maybe 9 with the HDMI connector?) | 8? | 4 | 4 (dual link SST) |
The two XDRs take up all four DisplayPort outputs of the 580X, leaving only the two HDMI 2.0 outputs free. Apple does not say whether or not you can use the HDMI 2.0 outputs. It may be possible. HDMI 2.0 has less bandwidth than DisplayPort 1.2, so you can only use 4K at 8 bpc. 4K 60Hz from HDMI 2.0 might use a chroma sub sampling mode instead of RGB so watch out for that - if it happens then there are ways to force RGB (by overriding the EDID of the display).
