External hard drive not visable with 2023 24-in iMac running Seqoia 15.5

I did not format the drive, a 4TB Western Digital MyBook for Mac which has served as my backup since 2016. My current 2023 24-inch iMac was recently purchased when my 2019 27-inch iMac failed and my Asurion Home Tech Protection plan's shop deemed it irreparable. The 2023 model was the newest I could purchase with the buy-out option money I was offered, and once I received it I just plugged in the iMac, then the Mybook, at first just plugging into one of the Realtech multi USB to USB-c adapter hubs supplied with the new computer. Then while troubleshooting this problem I read that it should not be plugged into any type of hub. So I purchased a Syntech USB C Male to USB 3.0 Female Adapter Compatible with Mac, which is now plugged directly into one of the USB-c Thunderbolt ports. When I still could not see the myBook in Finder I quit Googling for answers and came onto this Forum.

To answer your second question, the MyBook has its own power cord, it warms up and I can feel the disk spinning. After connecting using one of the adapters supplied with the computer, I connected the MyBook 9 (I believe it was into the first USB-c port) then went about to restore with the Time Machine restore process, which proceeded remarkably fast with no issues, other than the fact that not all programs and files transferred. So through Finder I accessed the Mybook visible in the sidebar and manually copied and pasted some data, files and applications for which I had an immediate need. MyBook was initially visible at that time, but vanished since. I really appreciate your time and hope this gives you the complete picture. I see in my emailInbox there is one more response from you. I'll open that next and respond with any more information you may have requested. Thanks again!

When it rains it pours. After rebooting my Mac was rejecting my password for god knows why and I could not restart. do just for grins I reset my password, even received notice of that on my IPhone and STILL can’t restart my computer. Eventually I got a great big yellow triangle telling me the Apple server was down and my request could not password rest could not be completed, and I may have to wait several days to regain access for my own “security.” I’m at my wit’s end!

OK, the Apple server finally connected and I got my computer back on. Immediately entered the command you sent me in Terminal after disconnecting MyBook and an external CD drive, re-connected and still nothing showing in Finder, even after opening a new Finder window.

Oh, really? Between first setting up my new iMac and now the WD MyBook died? What are the odds? Before getting on this Forum I thought my last resort would be yo have the same shop Asurion used to declare my 27-inch iMac irreparable take a look at the myBook to see if any data can be salvaged from it and put on a thumb drive for loading to my new iMac. You think that is my only viable option to pursue at this point? and if they declare the MyBook dead as well guess I'll make claim on that. At least Asurion will cover some of the cost for a new external hard drive, I think.

Not sure what you mean by output as I never use and not real familiar with the Terminal App. All I can tell you is I entered the command you provided and hit 'ENTER', but nothing happened. At this point I'm resorting to Mr. Spock's quote in Star Trek, "“Once you've ruled out the impossible, whatever remains, however improbable, must be true.”

Although a great coincidence, apparently my external hard drive decided to die immediately after my iMac. Thanks for your attempt to help. Guess I should have kept my Carbonite subscription.

UPDATE: Progress! My wife found nothing with the Disk Management App BUT did find the myBook with Device Manager (which says "this device is working properly, however could not see any actual folders and/or files that were backed up. I'm forwarding the last email notification linking your last response to her so she canrespond and relay to you firsthand what she is seeing in Device managers maybe you can guide her to the actual files that are backed up (things like Word and Excel documents, artwork created with CorelDRAW and many PDFs of bills, receipts, statements, etc.). Re: your comment about possiblya bad USB cord or adapter, her laptop shows a proper USB connection in her Device Management and that was connected to my Max with a brand new Syntech USB C Male to USB 3.0 Female Adapter.

When connected through USB to an HP, the drive shows up under disk drives in device management but not listed in explorer. Device management says the device is working properly. It is not listed in disk management.

Ok, the WD MyBook was indeed my backup operating with Time Machine on my Mac. Can you please tell me what would have to be installed on my wife’s HP laptop in order to read the MyBook folders and files I have backed up there?

"Assuming this is a Time Machine drive, Windows could not read the drive unless you had installed software to facilitate that.unless you had installed software to facilitate that. "

Yes, the MyBook external Drive was backing up my iMac using Time Machine. What software would allow us to read that when hooked up to my Wife's HP running Windows?

Perhaps I misspoke. The device I have is a Western Digital netbook for Mac. It was plug and play, no formatting. required. I just connected it to my Mac, opened Time Machine and chose the MyBook as the location for my backup files. Sounds like you are saying that make everything on the MyBook a "TM backup drive," requiring software that reads an APFS volume. Are you saying all the backups are in a format only a Mac can read, hence the need for us to install the Paragon software own my wife's laptop in order to read the APFS folders and files on the MyBook? If my understanding is correct should I be looking a purchasing the Paragon Mac Toolbox in order to recover my files? Or preferably, is there a way to get the MyBook back in my Finder sidebar and not have to buy anything?

I appreciate the advised caution, but if I can't access my files, accidentally editing a Word document, PDF or Excel spreadsheet hardly matters. Even if I accidental deleted something I can't access any of them now so I'd be no worse off! Are you familiar with th Paragon Mac ToolBox? Is that the type of software you suggested that would allow me to read and/or copy MyBook files to my wife's HP laptop and then transfer to my Mac from a thumb drive or other media?

When I launch TM without the MyBook connected I get a setup popup saying, "You haven’t selected a location for Time Machine backups." If I continue and try and specify the thumb drive where I pasted the last full backup found on the MyBook drive using the HP laptop with The Paragon Mac Toolbox software I purchased, the first step is to erase the thumbdrive so it seems like I'm going around in circles.