So, I finally updated my 2015 iMac (with SSD drive), still running Catalina, to Monterey. Unfortunately, it did not go well. When the install was over, I had all sorts of weird symptoms (e.g., trash would not empty). And the drives would not load in Disk Utility.
When I checked in Recovery mode, I found that the internal drive was in some half-way state, showing both the original drive partition and an “Update” partition. So I deleted all the partitions and started over fresh, restoring the iMac back to Catalina via my mirrored backup (using SuperDuper).
This went fine and I am now successfully back to where I started.
My question is: Should I hope that the install error was a one-tine glitch (or maybe my repartitioning fixed whatever the cause might have been) — and just try reinstalling Monterey again?
If not, what else should I do before trying to update?
P.S. As a last resort, I can just give up updating altogether — and wait till I get a new iMac later this year.
Follow-up: I finally decided to take action. First, I updated to a later version of Catalina (after I restored the drive, I found it was not the latest version). I continued to have a few odd symptoms. So I finally decided to upgrade to Big Sur (I still had a saved copy of the Big Sur Installer). That was completely successful. Everything is running smoothly now. No weird/odd symptoms at all! Given that, I plan to upgrade to Monterey in a week or so. At this point, I am optimistic it will go well.
As to the cause of the initial problems? I suspect I will never know. Just one of those glitches that occur from time-to-time when you upgrade the OS.
FYI, Apple makes installers for older macOS releases (latest version of each release) available from their web site, so there’s no need to save a copy of the installer if you don’t want to.
High Sierra (10.13) through Big Sur (11) are provided via links to the App Store.
Yosemite (10.10) through Sierra (10.12) are provided via direct downloads of disk images containing the installer package.