Yes I am using OCLPHi there.
iMac 2012 doesn't natively supports Ventura, so I'm assuming that you are using a patch.
You describe very slow access times, your iMac has feen fitted with a SSD disk or still have the original one?
I would start by booting from the CCC backup, (plug the disk, turn ON the Mac and immediately press and hold the OPTION/alt key)
If you can boot, then your iMac is probably working correctly.
Once logged, open Disk Utility and run First Aid on the internal disk, also check if there's some empty space available.
If not, you can delete the contents of the Caches folder (and empty the Trash folder) in the user library to quickly free-up some GB's.
If errors were found and corrected and/or the disk was full, you can try to restart and boot from the internal disk.
If the internal disk shows errors and they cannot be fixed by the Disk Utility, then you can have a faulty disk or a corrupted APFS volume.
A faulty disk will need a replacement
A corrupted one will need you to restore from a backup.
Before restoring, you can save your email folder (in User's Library) to have those emails safely stored.
No I don't have any slow access times. I have an SSD, it works flawlessly. This thread was borne out of just ONE problem. I tried to move aroudn 37,000 photos from one folder to another. Silly maybe, but it hung (as i half expected). I had to force quit and reboot. But that 'command' seems stuck in memory, hence after every reboot Finder just tries it again, which means it hangs again. I need to clear that 'command' out of the 'queue' somehow.
I believe Safe Mode will do that, i haven't got round to following the advice above yet to hopefully force the machine into Safe Mode. That may solve my problem.
I don't think there's any problem with my hardware at all. I am sure there isn't. It's just that Finder error/hang where it says "The last time you opened Finder, it was force quit while reopening windows. Do you want to reopen its windows again?"