trs96
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- Joined
- Jul 30, 2012
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- Motherboard
- Gigabyte B460M Aorus Pro
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- i5-10500
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- RX 570
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I think I've come across the reason for this. In looking back at the 2013 iMacs which were dropped from support in Big Sur, I noticed that the 21.5" iMac from Late 2013 used Iris Pro 5200 as the primary GPU. Apple never used HD4600 as primary in any Mac sold during the Haswell era of 2013/14. That means that the Macs with HD4600 iGPU only used those graphics as headless in combination with the Nvidia discrete graphics such as the GT 750M. Hence, "use of this PlatformID (0x04160000) will result in either no output being sent to the monitor or glitchy behaviour."Special note on desktop HD 4600 IGPU: If you have a Haswell CPU with a HD 4600 IGPU and no dGPU (IE: solo IGPU system) then one would assume that you would use the Intel HD 4600 PlatformID of 0x04160000 as detailed in the Haswell section this post. However from my experience it seems that use of this PlatformID will result in either no output being sent to the monitor or glitchy behaviour. You may have different results but it did not work for me on three different HD 4600 systems. After some trial and error I found that setting the PlatformID to 0x0D220003 (Intel Iris Pro Graphics 5200) and device-id to 0x0412 (Intel HD 4600) with the iMac 14,2 SMBIOS works very well for solo HD 4600 IGPU
Only Intel HD5000 graphics are still officially supported in Bug Sur. It will be interesting to see if we can still use HD4600 graphics by changing platformID to 0x0D220003 as we have always done in macOS versions up to Big Sur.
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