I'm facing the same "black screen" issues in Chrome, in Safari and in some Apps.
Hardware: Z370 Aorus Gaming 5, I7 8700k and the Asus Strix ROG Vega 64 OC.
I'm running the Vega as my main graphics card but have the IGPU activated for Quick Sync etc. (using Lilu+Whatevergreen for
ID and framebuffer injection).
I have only one screen connected on the DVI port of the Vega 64.
I have created a custom KEXT for the fans.
Interesting thing is, that on some specific websites in chrome the screen goes black. If I close the tab with the keyboard again, the black screen goes away and I see the desktop again.
Deactivating the hardware acceleration in Chrome or Safari is really not a great solution as it also happens in some apps where I can not disable hardware acceleration.
Could it be somehow in connection with the IGPU? Maybe for some reasons when using the hardware acceleration in some apps the system switches the output to the IGPU and the screen goes black on the Vega?... I could not yet test that possible scenario.
I'm desperate for a solution and are open to try everything ;-)