Enable AMD HEVC support for Vega GPU, same as RX 4XX/5XX but does not need X4250 dummy injector (Vega HEVC native supported by macOS), need SMBIOS supported by AppleGVA and GPU is attached to device GFX0, check GPU status with IORegistryExplorer.app.
For SMBIOS unsupported or limited support by AppleGVA like MacPro6,1, need edit/add properties to AppleGVA info.plist or install shiki.kext and add boot arg shikigva=32, it will replace board-id to iMac14,2 by default.
If GPU is not attached to device GFX0, use custom ssdt.aml change device to GFX0, or try rename PEG0 to GFX0 from Clover Acpi patch, or install WhateverGreen it will auto rename device to GFX0.
Pls notice that recently AMD H264 decoder is buggy, if you are using FCPX do not share/export file as H264 and output as HEVC instead, install Compressor.app to support HEVC output then add “Apple Devices 4K (HEVC 8-bit)” to FCPX Share/Add Destination as below.
View attachment 309916