External hard drive woes after installing Sequoia

Thanks BDAqua. I can back up by using a Spotlight search to access folders and files (I cannot access files using finder, this is part of the problem) and then dragging those folders and files to another disk. It'll take quite some time. And it will be interesting to see if the folders and files from the faulty disk are corrupted in any way.

Thanks for your quick reply, BDAqua. Much appreciated.

I booted into repair mode [Cmd-R] and tried fsck from there. The result was, 'No such file or directory'. However, in Disk Utility the offending disk is visible. I tried ** in Mac Repair Mode but no luck. Same report as above.

Thanks again, BDAqua. I did as you advised. When I ran Disk First Aid on the Container Disk, I had to scroll down 3 times to see the full report. I have almost no understanding of what this report means and, as screen shots are not possible in restore mode, I took photographs of the screens. They are attached. Likewise with the Data disk (which I'm guessing is causing the problem) but the report was much smaller. A photograph of that is also attached.

Thanks again, BDAqua. I'll follow your links and report back.

What is really weird is the fact that using Spotlight I can access the offending disk. I can move files from it and - if I've accessed the disk through a Spotlight search and then clicked on its icon in the Path Bar - I can move files onto it. But I can do none of this using Finder. I wonder why? Why can Finder not access this disc but Spotlight can?

Thanks, Old Toad. I did as you suggested but - as far as I can see, struggling to make sense the logs - the response was identical to using ** in recovery mode. And, as you said, a long shot.

Thanks for your reply, Ian. I don't have DriveDX installed. I was thinking of buying it but your comment suggests that I should not.