I have a 2017 27" iMac that originally had a Fusion HD. That drive died, and I replaced it with a 2 TB SSD. I haven’t installed Monterey yet after reading the issues people have experienced who don’t have the original SSD drives on their computer. After reading a reddit thread, I started wondering whether my concern on this issue was misplaced. I am curious whether any of you have experience installing Monterey on a computer that originally came with a Fusion drive and now has an SSD and how that installation process went.
Without knowing exactly what that Reddit thread had to say, I can’t accurately comment on it, but all of the other reports on bricked Macs after attempting a macOS 12.3 update (including the TidBits article) are saying it only impacted 14 and 16 inch MacBook Pro’s that had their entire logic board replaced. Nothing about iMacs or their internal drives.
Although I have the same iMac model as you, my 2TB SSD came with it, so my experience doesn’t count. Hopefully someone else who went through your experience will eventually comment.
From the comments here (and elsewhere) the installation problem appears to be occurring on any Mac computer which does not have the original Apple SSD drive still installed and which now has a third party SSD. I don’t have a huge amount of tech knowledge, but my question arose because a Fusion drive in my mind isn’t really an SSD drive. I understand there is a small SSD combined with a spinning disk drive but I haven’t read anyone saying they experienced problems upgrading after replacement of a Fusion drive, only with replacement of an SSD.