I would like to say a huge thank you to RehabMan, for his incredible work and dedication to this community.
I will describe my setup for other early tester of Mojave with unsupported Nvidia card who wants to keep it installed for dual boots or any other reasons.
So, I've updated a perfectly working 10.12.6 (smbios was 14.2, now 15.1 since few months) to Mojave on my desktop but was stuck with a black screen problem, mostly because my pcie slot 1 is occupied by a watercooled 1080ti I wanted to keep in place, but because it's not (yet?) supported, I added a cheap HD7850 (Mojave sees aR9 270) in second slot. I have three monitors, 2560x1440 native resolution, 1 connected to the 1080ti (HDMI), 2 to the R9 (DP and DVI) and had these various results with Mojave:
- 1080ti alone with High Sierra webdrivers: display OK but, of course, no acceleration, Sleep/Wake OK
- 1080ti with High Sierra webdrivers and R9 2770: black screens (so used remote desktop), Sleep/Wake OK
- 1080ti without webdrivers and R9 270: no display from the 1080ti but R9 was OK, Sleep OK, Wake cause reboot
I was searching for a way to disable the 1080ti in Mojave and discovered
RehabMan laptop specific guide, then this
specific post regarding desktops which brought me here. I've just created the SSDT-DiscreteSpoof.aml file, uninstalled the Nvidia webdrivers, crossed fingers and rebooted... WOW, it really works!!! No more black screen, the Nvidia card disappeared from the "System report", only the R9 is detected and, most important, Sleep/Wake is working perfectly!
So,
@flymovies, don't hesitate, it's the way to go, and, again, my deepest gratitude to RehabMan.