I have successfully installed Mojave 10.14.5 on my Optiplex 3040. I used the vanilla method using WEG and display 1219 as so:
AAPL,ig-platform-id = <00001219>
framebuffer-fbmem = <00009000>
framebuffer-patch-enable = <01000000>
framebuffer-stolenmem = <00003001>
This 3040 has one DP and one HDMI port. I have identical HDMI monitors hooked to these ports (one is using a DP-HDMI cable obviously). If I boot with both monitors I get a display on the DP output, nothing on HDMI. If I unplug the DP cable, I get display on the HDMI port. I have attached my IOReg file when booting with both attached, note that display0 is attached to framebuffer2, port 0x6, type 0004. When I boot with just the HDMI port connected, display0 moves over to framebuffer1, port 0x5, type 0008. HDMI audio works fine using either port.
I have read about putting in additional device properties so WEG can connect the ports but have been unsuccessful (over my head). For example, I used Jake's 7040 plist,shown here:
#framebuffer-con3-alldata = <03060a00 00040000 87010000>
#framebuffer-con3-enable = <01000000>
AAPL,ig-platform-id = <00001219>
device-id = <12190000>
enable-hdmi20 = <01000000>
framebuffer-con1-alldata = <01050900 00080000 87000000>
framebuffer-con1-enable = <01000000>
framebuffer-fbmem = <00009000>
framebuffer-patch-enable = <01000000>
framebuffer-portcount = 4
framebuffer-stolenmem = <00003001>
framebuffer-unifiedmem = <00000080>
I booted with framebuffer-con3* commented and uncommented, neither way worked. This pc has two DP and 1 HDMI though. Some are successful doing Kernel patching AppleIntelSKLGraphicsFramebuffer.kext but that didn't work and maybe that technique stopped working with later versions of Mojave?? I'm hoping someone can provide the device properties I need to put in config.plist to get both monitors working. Thanks!
iMac.ioreg.zip config copy 2.plist.zip