Thank you for your response.
You correctly understand that the the Seagate drive works perfectly on the iMac running Big Sur.
Connecting the Seagate to 2016 MacBook Pro, the Mac OS Ext shows on desktop instantly but the APF containers take an age. Initially When viewed in Disk Utility two volumes could not be mounted, but they are now mounting, albeit slowly. The drive would not respond to Eject either singularly or offer Eject All
I have a Le Cie SSD external drive onto which I had recently cloned my Data using Carbon Copy Cloner before upgrading to Monterey. That drive works perfectly when connected to MB Pro.
Some developments; a friend arrived clutching the latest SanDisk extreme pro portable SSD (2,000 MB/sec) and out of the box it connected to my MBPro and worked perfectly - the speed mind-blowing.
I have connected the Seagate drive. The Mac OS Ext showed immediately with long delay before the 3 APFS volumes, but they all mounted OK. I have been able to access more folders though trying to open individual file results in spinning ball with over a minute to open a Word doc (apologies not Pages!), so beginning to conclude indexing may be what’s needing to resolve itself. When I tried to eject, this time after a delay I did get the Eject All offer and took it, with no response so looked at one or two more folder contents when I got message could’t eject because…. But actually all disc icons had left desk top. In the end I accepted the force eject offer for each volume.
Rebuild Spotlight. Whilst reading instructions I had reconnected Seagate which was taking for ever to mount the APFS volumes. In the Preferences>Spotlight, the privacy tab window was empty but after several minutes the 3 volumes mounted and one of them showed up in the Spotlight Private window. I has a suspicion that this might be the offending volume so selected it and deleted it and will now leave connected to re-index and go and do something else - adding insulation to the loft!
OK back having left plenty of time to Index the one volume. Ejecting worked correctly. When I reconnected the drive the Mac OS Ext mounted instantly the three APFS volumes after 45 seconds, but all seem to be OK.
I no longer need the empty Mac OS Ext partition son thought I would reformat APFS. That actually failed , reporting.
Erasing “Mac OS Ext” (disk2s3) and creating “New APFS”
Unmounting disk
Erasing
Initialized /dev/rdisk2s3 as a 465 GB case-insensitive HFS Plus volume with a 40960k journal
Mounting disk
Creating a newempty APFS Container
Unmounting Volumes
The volume “New APFS” on disk2s3 couldn’t be unmounted because it is in use by process 88 (fseventsd)
Couldn’t unmount disk. : (-69888)
Operation failed…
Googling suggested this could be a hangover from an older Mac OS so I erased and reformatted Mac OS Ext and then erased and changed to APFS and this time success.
Interestingly that reconnecting disc, the new empty APFS mounted instantly whilst the other volumes again the best part of 50 seconds. They mount instantly on the iMac.
I will now re-index the two other volumes and see if that speeds things up further. Still, now working if somewhat sluggish and the Finder has had had no problems so definitely getting there.
