Is there a prereq BootROM version? I did not check beforehand, but after I applied this, I checked and I am at Boot ROM Version: 157.0.0.0.0
Your system firmware was not updated unfortunately. This is another data point that appears to confirms our suspicion that you have to be on some yet to be determined system firmware version (160.0.0.0 and higher on MacBookPro11,1?) that came with macOS Catalina 10.15.x. To update the system firmware to the minimum version, you will have to use an Apple SSD.
Hey CMD+Q, what if I want to flash a MacBook Pro whose identifier ends in .fd? [...] Will the .fd files work the same way? Just bless them and power down/boot?
Yes, I do not have access to a newer system to try this myself; however, these "Secure Capsule" files (Pre-2015 Intel MacBooks?) and "Firmware Descriptor" files (Post-2015 Intel MacBooks?) are functionally equivalent for our purpose.
how does one got from 199 to 457? That's a big numerical difference!
The system firmware update is typically initiated by a macOS update; but can also be started outside of that process via
/usr/libexec/efiupdater
which in turn uses
/usr/sbin/bless
with the 'private' firmware update function. See post
https://forums.macrumors.com/thread...ook-pro-ssd-to-m-2-nvme.2034976/post-29249031 for that process. Those instructions assume you extract the firmware files from the Big Sur installer and place them on your desktop. I know
@otosan prepared another method in post# 7760, but I am always careful with third-party payloads; no offense.
I'm wondering if the Bootrom itself may be what causes some MBPr 2013 - 2014 to brick… is that naive?
Last time I checked the support article on this issue, it sounded like the MacBooks were not bricked but were rather hanging in some stage after the firmware upgrade. I could be wrong.
However, I'm super excited to update the Bootrom without upgrading the OS. Just for clarification: Is it safe to do this with the NVMe drive or do I have to swap it for the original Apple SSD?
It appears that whether you are able to upgrade with a third-party SSD in place depends on your system firmware version; per the last few comments on this issue: Some people have been successful, some have not.
Also, has anybody done the trick since Apple stopped the rollout of Big Sur on older machines? Does the installer in the MAS still contain the necessary files for my MBPr 13" late 2013?
I have updated your exact model to system firmware version 427.0.0.0.0 that came with the the macOS Big Sur 11.0.1 (20B29); while still running macOS Catalina. From what I can see in the respun build 20B50 of Big Sur, the updated MacBookPro11,1 firmware is still included (same version number) but the macOS upgrade itself appears to be blocked.