- Yes: Nvidia graphics supported after root patches
- You may be able to disable iGPU using WhateverGreen.kext. Read more
here. This will require manual "surgery" on your Open Core config.plist and manual addition of the WhateverGreen.kext to your Open Core EFI. You'll want to look at the WhateverGreen.kext boot-arg -wegnoigpu or the DeviceProperty disable-gpu (use one or the other). Explaining how to perform the "surgery" is off-topic in this thread and learning how to perform the "surgery" is important for you to know how to maintain your Mac, because you will need to manually apply this change after every "Build and Install Open Core"
- I have seen cases where the quality / type of video cable affects graphics performance, but I don't think this is what is forcing the iGPU. Not certain though. Before you buy a new video cable, test WhateverGreen first.
If my explanation of Open Core, WhateverGreen, kext, boot-arg ... are new to you, you will need to be patient and learn about Open Core which your unsupported Mac is now using to boot Sonoma.