Seagate Expansion Drive not displaying

I am using a Macbook Pro. My expansion drive is configured to be useable with Time Machine [i.e. Mac only]. I have been using another expansion drive in my troubleshooting, which has also been configured this way.

My Seagate external 'expansion' drive is not showing up in the Devices of my computer (aka under Devices in the sidebar, in Finder), and I cannot access the files on it.

When I plug it in, the blue light flashes for a little while, then stays blue. I can feel and hear the disk spinning inside it. As per the attached screenshot, it shows up in Disk Utility and System Report on my MacBook Pro, but incorrectly shows as being full to capacity. As per the attached screenshot, I have ensured it is visible in Finder Preferences.

I have tried another Seagate 'expansion' drive [SN: NA81Y5D1] and it displayed and the files were accessible.

I have tried using a different cord to connect my expansion drive to my MacBook (the cord from the other Seagate expansion drive) and my expansion drive did not display.

I have tried plugging BOTH expansion drives into a PC computer [the only other computer in the house] and my expnsion drive did not display as being accessible or as having the divers installed [it was visible but the files could not be accessed] - while the other expansion drive showed the drivers as being installed.

I have tried restarting the computer, with and without the expansion drive attached, with and without the power cord.

I have tried repairing my expansion drive in Disk Utility.

I have tried starting up my MacBook in Safe Mode.

I have tried repairing my expansion drive in Disk Utility in Recovery Mode.

I have tried resetting the SMC on my MacBook.

I have tried all relevant suggestions in this post: Seagate External HDD won't show up.

This hard drive was working with this computer, yesterday......

Thanks in advance!