System Details

• Model: Mac mini (Late 2009)
• Original macOS: OS X El Capitan (10.11.6)
• Previously running: macOS Monterey and later Sequoia via OpenCore Legacy Patcher (OCLP)
• GPU: Non-Metal
• Bootloader: OpenCore (suspected corrupted)

Issue Summary

After running macOS Monterey / Sequoia via OCLP, the system crashed and is now unable to boot or reinstall macOS. The Mac appears stuck in a corrupted OpenCore / EFI state where neither Recovery nor external installers can fully take control of the system or internal disk.

Observed Symptoms

• Selecting Install macOS Monterey (internal or USB) results in Apple logo with progress bar that never advances (stuck for hours).
• ⌘R no longer reliably boots local Recovery.
• ⌘⌥R / ⌘⌥⇧R Internet Recovery intermittently fails or redirects back to local Recovery.
• Boot picker (⌥) shows EFI and Recovery; EFI appears to be OpenCore.
• Booting Recovery does load macOS Utilities, but disk operations fail.

Bootable Installer Attempts

• Created and attempted to boot from:
  • macOS Monterey USB installer
  • OS X El Capitan USB installer
• Both USB installers appear in the boot picker and can be selected.
• Monterey USB freezes at Apple logo (same behavior as internal installer).
• El Capitan USB boots, but disk erase and install still fail due to disk management errors.

Terminal / Disk Errors Encountered

• error -69888 couldn't unmount disk
• Resource busy
• could not find disk for disk0
• could not start up disk management session

These occur even when booted from Recovery or a bootable USB, indicating disk arbitration (diskmanagementd) cannot start or release the internal drive.

Troubleshooting Already Attempted

• PRAM/NVRAM reset (⌥⌘PR)
• Local Recovery, Internet Recovery, and boot picker selection
• Bootable USB installers (Monterey and El Capitan)
• Forced unmounts via Terminal
• diskutil eraseDisk using multiple disk identifiers
• Unloading diskmanagementd
• Raw disk erase attempts (rdisk)
• Multiple reboots and power resets

None of the above succeeded in erasing or releasing the internal disk.

Current Assessment

The system appears stuck in a state where:

• OpenCore intercepts or influences boot even when selecting Recovery or USB installers
• Recovery and external installers are still partially tied to the internal disk
• Disk arbitration services fail to initialize
• Software-only recovery is no longer possible

At this point, the only reliable recovery path appears to be physically removing the internal SATA drive, erasing it externally on another Mac, then reinstalling macOS clean (El Capitan)

TL;DR:
Late-2009 Mac mini previously running Monterey/Sequoia via OCLP crashed and is now stuck in a corrupted OpenCore state. Monterey installer (internal + USB) freezes at Apple logo. El Capitan USB boots, but Disk Utility and diskutil can’t erase the internal drive (-69888 couldn’t unmount, resource busy, disk management session failed). ⌘R unreliable, ⌘⌥R Internet Recovery doesn’t fully bypass OpenCore. Even from Recovery/USB, disk arbitration won’t release the internal drive.

I DONT KNOW WHAT ELSE TO DO AND ITS DRIVING ME CRAZY