In later iterations of MacOS 10 and MacOS 11, Apple’s install would not always update the firmware of systems using 3rd party NVMe storage-even if the operating system itself was installed properly. Could there be a problem with this? But how to update SAMSUNG SSD? Otherwise, the installation simply halts, and the computer boots from the System Volume and the old OS, with 'MacOS Installer' listed as a bootable option on the manual boot screen. Interestingly, attempted to load from Recovery (booted from the external SSD) resulted in the '.firmware.' popup message that others with non-OEM hardware have reported. Unfortunately, that resulted in copying an unbootable copy of 12.0.1, and a whole host of other problems (that I've since resolved). I was able to force the installer to close by running it from the external SSD, with the computer booted from that drive (i.e., Method 3). Interestingly, only Method 3 (not recognized by Tech Support) actually ran to completion (and removed the 'MacOS Installer' from the boot menu). It appears that the installer fails to complete the installation, as 'MacOS Installer' is still included on my manual boot ('Option' key) screen, and 'Macintosh HD', the System Volume still includes Big Sur.

Typically, the failure mode involves the installer running until the 'restart' phase, and then after two restart attempts, the installation dumps to the 'Macintosh HD' boot volume, and boots up in Big Sur. 'Supported'? I believe three of the four methods I described are supported (Method 3 is not), and in fact recommended by Apple Tech Support. I'm trying to start a new thread on the NEW PROBLEM. I have seen a couple other posts on this issue, but no evidence of progress, as the original thread addresses a different issue. There is another thread here addressing failures to install on machines with aftermarket internal drives, but that does not apply here. I finally deleted the 'Macintosh HD' data, and reinstalled Big Sur from Recovery mode on the internal disk. This resulted in all subsequent attempts to work backwards to Big Sur failing since the machine 'thought' that MacOS 12.0.1 was already installed. When I installed from the external SSD running Monterey, it actually wrote the OS to the 'Macintosh HD' sector on the internal drive, but would not boot. I've tried the following: 1) install from System Preferences/Software Update, 2) install from bootable USB installer, 3) install from external USB SSD running Monterey on my iMac (so, the machine WILL run Monterey), 4) install from Recovery mode, and all fail.

The OS 12.0.1 installer fails to install on my machine. I have a 2017 iMac 18,3 with all Apple OEM hardware, running Big Sur 11.6.1.

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