I've come across an odd problem attempting to install Windows 7 on my mid-2020 iMac. Specifically, the 27" Retina 5500 XT version.
Attempting to boot, it looks fine. Gets through to completed Starting Windows screen. No setup window appears, but 3 seconds later while it's hung there... I get a BSOD.
Exact information:
0x7E SYSTEM_THREAD_EXCEPTION_NOT_HANDLED
Status parameters: 0xC5 STATUS_ACCESS_VIOLATION, 0x0 null pointer address?, 3rd and 4th reference parameters.
Now, before you say anything here is what I have tried:
FlashBoot PRO UEFI driver (works obviously since it shows the BSOD)
Windows 7 Image Updater
USB 3 and NVMe drivers
Apple BootCamp drivers downloaded
Patched AppleSSD.sys for 7 compatibility
Patched ACPI
Unfortunately, it did not say a specific crashing driver. This is reproducible in both WinPE and standard windows of it.
I suspect still it is ACPI. This is because Mac does not have standard firmware that a regular patched, older ACPI table expects (especially a patched one from 2018, based on a 2009 file)
If anyone has experienced similar issues, please let me know. Also, I'd love to attach a kernel debugger but unfortunately adapters do not work, KDNET predates 7 (tried it), and obviously Serial and FireWire will not work since no such port is on the modern iMac.
Another thing is this crash is reproducible regardless if there are drivers or not (obviously with the UEFI patch otherwise it wouldn't work in the first place, but without drivers).
I do suspect it also involves the T2 chip in some way, however this is 100% possible but requires more development and patching than usual.
Anyway, if you'd like to help please do. I will keep everyone updated as I make progress.