iGPU acceleration not working with headless dGPU setup

• CPU: i7-8700 (with iGPU UHD630)
• dGPU: Radeon RX 5700 XT
• SMBIOS: iMacPro1,1
• Bootloader: OC 0.8.4
• OS: MacOS Catalina 10.15.7
• All kexts are up to date

I'm using the dedicated gpu (dGPU) to drive the display. I can see the iGPU in Hackintool and Intel Power Gadget. However, when watching a video, previewing it, opening preview and doing things that should require acceleration, there is no activity in the GFX line.

I've used the official guide of Dortania and Whatevergreen. As I'm using the dGPU mainly the only line that I added was

<key>DeviceProperties</key>
<dict>
<key>Add</key>
<dict>
<key>PciRoot(0x0)/Pci(0x2,0x0)</key>
<dict>
<key>AAPL,ig-platform-id</key>
<data>AwCRPg==</data>
</dict>
</dict>
<key>Delete</key>
<dict/>
</dict>

It seems that I don't need framebuffer properties.

Any hints on what should I add?