Undervolting a i5-12400F on a Asus B660M-A D4

Sorry to hear that… i dont have that mb or know the bios items present.
The package time is not the issue here but helps a bit.
The crucial part here, is the PL1 and PL2 delivery power package to the processor.
Presumably the system is well assembled?!??! A lot of those correctly “assembled” machines come to me with heat problem’s, 11th Raptor Lake and 12/13th AlderLake
Anyway, at your risk, you can try mod bios but this mb model doesn’t have USB BFB feature…

[TOOL] UEFI Editor - BIOS/UEFI Modding / BIOS Modding Guides and Problems - Win-Raid Forum (level1techs.com)

[GUIDE] [UPDATE] Usage of AMI’s AptioV UEFI Editor + FPT Flash Method - BIOS/UEFI Modding / BIOS Modding Guides and Problems - Win-Raid Forum (level1techs.com)

Any issues regarding the linked threads, post there not here, Good luck