As you may or may not know, 400- and 500-series mainboards are compatible with both Intel Comet Lake (10th gen Intel Core) and Rocket Lake (11th gen) CPUs. But when combining 10th Gen Intel Core CPUs with the newer 500-series mainboards, this causes issues with the UHD 630 iGPU in macOS.
NOTE: Rocket Lake's Intel UHD 750 iGPU is not supported by macOS! So don't combine an 11th gen Intel Core CPU with a 400-series mainboard!
The UHD 630 is correctly detected by macOS and can be used for Intel Quick Sync Video (IQSV), but the video outputs don't work.
Fix: None yet. Under investigation.
When using an empty framebuffer, such as 0300C89B, VDADecoderChecker will report that "Hardware acceleration is not supported" (so does VideoProc Converter: "H264 unsupported").
The HEVC decoder on the other hand works fine with an SMBIOS that supports iGPUs, such as iMac20,1.
Fix: Use an AAPL,ig-platform-id with connectors, such as 07009B3E and reboot. After that hardware acceleration should work.
- FishyFlower for his explanations