Black screen after boot with Intel Graphics

I'm running this build with this config.plist currently on 10.14.6, and everything seemed to work perfectly, except for one thing: the intel GPU.

Now, this is not a problem in most programs; just disable internal graphics in the bios, and let the amd card do everything. Except it now turns out that iMovie really wants that Intel chip, so now I have to get it working. However, when enabling it iMovie simply crashes every time you launch it, so something went wrong there.

Naturally, the first reaction is to physically remove the AMD card and try to run on Intel alone, but that has resulted in some strange behaviour:

• On regular boot, it will seem to boot normally, and then cycle between a black screen, a black screen with a mouse pointer in the top right corner, and a black screen with the grey spinning loading icon, seemingly forever.
• On a verbose boot, it will seem to boot normally, then after the point it would normally go into userland, it will have two more clean print statement sessions, the last one saying that GTK in installed.

Note that "black screen" in this case does not mean that there is no display signal, but that the signal tells the display to be entirely black.

Also note that the display is a 4K monitor connected over a displayport cable.