Hi,
Sorry i'll send my debug files and more infos tomorrow too.
What i can say is that i tried many things today:
-No more luck with AptioMemoryFix. I tried to change all Bios settings required (CFG Lock disabled, CSM disabled, Fast Boot disabled, VT-d disabled, SGX disabled, Above 4G enabled) i only couldn't change XHCI/EHCI Hand-Off values because the vars associated are very generic and therefore too dangerous to change with modified Grub i think.. By default XHCI Hand off is On and EHCI Hand Off is Off.
I ran VerifyMsrE2.efi, nothing seems wrong. Ran CleanNvram.efi and set PowerNap off. No change
I finally replaced back AptioMemoryFix by OsxAptioFixDrv because i was tired of having to shutdown with hard button. AptioMemoryFix seems to keep NVram values fine but avoid a proper shutdown for a reason i ignore.
-I tried to change some Bios System Agent Graphics settings like Primary Display (SG to IGPU), or ACPI ALS On. No Change. Reverted back.
-I updated DSDT.aml to ignore ACPI0008 Ambient Light Sensor, and also tried to create a fake ALS, as seen in Rehabman's Backlight Guide. No more luck
-I tried to use all known CoffeeLake platform-ids. No more luck. Went back to 3e9b0000.
-I was also annoyed because the black screen happened right after Clover selection screen, even before the Ramdisk message appears, so no verbose possible.. So i removed SetIntelMaxBacklight option in Clover. And first interesting thing, the verbose is now shown and the black screen only happens at the end of verbose. So i do think this is related to backlight, more than ever!
Second thing, even without this option, the backlight is functional and on apparent full max value when screen start!
Apparently we both had issue using AppleBacklightInjector.kext first, because the max value was too low. Even by using SSDT-RMCF and entering 0x56c for LMAX. And so using IntelSetMaxBacklight option helped us retrieve a good max value. But when it is recalled during boot, it creates the black screen issue. By removing the option the value is still kept anyway (as long as i don't use back AppleBacklightInjector).
I understand full backlight support would be better using AppleBacklightInjector, but for now i don't know how to set a correct max value with it.
-I also realised that, by removing Whatevergreen kext, the system sometimes boot without black screen issue at all and with backlight control working!
But sometimes only, not everytime, and i really don't understand why... This seems very random to me and i need to test more tomorrow to try to determine the exact case is fine.
I saw this fine start happen many times, on both my High Sierra and Mojave Beta 8 installs. Always on fresh start, not on reboot, and never with whatevergreen loaded. Maybe Whatevergeen is also loading a backlight value?
-Finally i have randomly boot issues like "kextd stalls", concerning IntelFramebuffer mostly, on Mojave Beta. Never on High Sierra.
That's all for today!