Hello. Some motherboards for AlderLake 12th Gen CPUs dont have option to enable AVX-512 when all E-Cores are disabled (currently, only ASUS and ASRock BIOS allow this). If you are eager enough to mess with it, you'll need to find UEFI module which modifies 0x000000AF MSR contents (yes, its undocumented MSR for disabling various AVX features). In case of Gigabyte, modules you need to patch is GenericComponentPeiEntry and SiInitFsp. Bit0 for disabling both AVX2 and AVX-512 features, Bit1 is for AVX-512 disabling. So, if you have 0xAF=0x2, then only AVX-512 is disabled. Here is example of patching needed for both modules for Z690 based Gigabyte motherboard (beware, you need to disable E-Cores before flashing modified BIOS):
1) GenericComponentPeiEntry changes:
LAB_0000d738 XREF[1]: 0000d72a (j)
0000d738 0f b7 c6 MOVZX EAX ,SI
0000d73b 83 e2 fc AND EDX ,0xfffffffc
0000d73e 03 c0 ADD EAX ,EAX
0000d740 0b c2 OR EAX ,EDX
0000d742 0b c7 OR EAX ,EDI
0000d744 83 e0 03 AND EAX ,0x3
0000d747 83 65 f4 AND dword ptr [EBP + local_10 ],0x0
00
0000d74b 89 45 f0 MOV dword ptr [EBP + local_14 ],EAX
0000d74e b9 af 00 MOV ECX ,0xaf
00 00
0000d753 8b 55 f4 MOV EDX ,dword ptr [EBP + local_10 ]
0000d756 8b 45 f0 MOV EAX ,dword ptr [EBP + local_14 ]
0000d759 0f 30 WRMSR

Change 83 e0 03 AND EAX ,0x3 to 83 e0 03 AND EAX ,0x3

2) SiInitFsp
00003be9 55 PUSH EBP
00003bea 8b ec MOV EBP ,ESP
00003bec 51 PUSH ECX
00003bed 6a 00 PUSH 0x0
00003bef 8d 45 fc LEA EAX => local_8 ,[EBP + -0x4 ]
00003bf2 33 c9 XOR ECX ,ECX
00003bf4 50 PUSH EAX
00003bf5 6a 00 PUSH 0x0
00003bf7 33 d2 XOR EDX ,EDX
00003bf9 41 INC ECX
00003bfa e8 23 3c CALL
00003bff 8b 45 fc MOV EAX ,dword ptr [EBP + local_8 ]
00003c02 83 c4 0c ADD ESP ,0xc
00003c05 c1 e8 1a SHR EAX ,0x1a
00003c08 24 01 AND AL ,0x1
00003c0a 8b e5 MOV ESP ,EBP
00003c0c 5d POP EBP
00003c0d c3 RET

Change 24 01 AND AL ,0x1 to B0 00 MOV AL ,0x0

Few more hints:
1) Gigabyte Q-Flash+ on Z690 boards could flash your modified BIOS
2) I had success with GenericComponentPeiEntry module replacement only with MMTools, all the images made by UEFITool made system non-bootable
3) I would recommend setting up all the bios settings, then use Q-Flash BIOS tool to backup your current bios, then modify it with those patches. Backup made with Q-Flash has your actual bios settings inside.


WBR, Mike