Resolving Downgrade Blocks in OCLP
Preflight Error 21 occurs when you try to install an older version of macOS (like Monterey) over a newer one (like Sequoia) because the system detects a firmware conflict.
The Fix:
- Full Drive Wipe: You cannot 'downgrade' in place. You must boot from a Monterey USB installer, open Disk Utility, and erase the entire internal SSD.
- NVRAM Reset: Perform a triple NVRAM reset before starting the install to clear the Sequoia boot variables.
- OCLP Version: Use the OCLP version that matches the OS you are trying to install (e.g., use OCLP 1.5.0 for Monterey).
Original Question: "Can someone please help me with this error I’m getting during root patching?"
 | https://youtu.be/sTDriSQm5eg?si=J5beUNiQB4sqr3JD I followed this video until the very end and then I get this error. Anyone have any ideas? Trying to install sequoia on a 2015 iMac btw. [link] [comments] |
![[link]](https://i.redd.it/ha0pzsajw22h1.jpeg){kind=link}
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