UHD 620 (Comet Lake Laptop) no screen output but USB-C monitor working

I finally managed to boot into macOS with HW acceleration by using this config:

​

<key>PciRoot(0x0)/Pci(0x2,0x0)</key> <key>framebuffer-stolenmem</key> <data>00003001</data> <key>disable-external-gpu</key> <data>AQAAAA==</data> <key>device-id</key> <data>16590000</data> <key>framebuffer-fbmem</key> <data>00009000</data> <key>device_type</key> <string>VGA compatible controller</string> <key>hda-gfx</key> <string>onboard-1</string> <key>framebuffer-patch-enable</key> <integer>1</integer> <key>enable-hdmi20</key> <data>AQAAAA==</data> <key>AAPL,slot-name</key> <string>Internal</string> <key>AAPL,ig-platform-id</key> <data>0000C087 </data> <key>model</key> <string>UHD620 as Iris+ 655 - (for DVMT=32M, no4K)</string> <key>framebuffer-unifiedmem</key> <data>00000080</data> 

​

The Problem now is that while macOS successfully starts, I do not get any output on my Laptop Screen after the first few seconds of verbose.

If I plug in a external USB-C Monitor I can navigate macOS and check that HW acceleration is indeed enabled.

What is the missing link here?