After posting my initial replies I remembered a problem I had with an external USB hard drive. tl;dr, the issue was with the USB interface in the enclosure, not the physical drive. I am not sure if my problem was the same as yours, but more detail can be found below.
The drive in question would randomly unmount, cause OS X to say it needed initialising and would sometimes stop my laptop from booting. The drive was not that old but I just kept having problems with it. After getting more frustrated with the drive (and wanting to get some data off it) I eventually pulled the enclosure apart and found the the drive inside was a standard 2.5" SATA drive. I put it in my USB disk dock (similar to this one, https://www.amazon.co.uk/TeckNet-Docking-Station-Tool-Free-Installation/dp/B00IS7Y96I/ref=sr_1_3?dchild=1&keywords=usb+disk+dock&qid=1593013408&sr=8-3) and the drive mounted and worked without a problem.
Having got the data off I formatted and partitioned the drive several times, copied data to and from it, and rebooted the laptop without any issue. I then put the drive back into the original enclosure and the laptop would not start with it connected, it would unmount at random and OS X would sometimes want to initialise the drive.
From what I could see the drive was OK but the USB interface in the enclosure had some sort of defect. Having pulled the enclosure apart I felt I could not really ask for a replacement, and as the drive seemed OK I ordered a USB disk enclosure. The drive is still working today and I use it to move large video projects between work and home. Since I put the disk in a new enclosure I have not had any problems (am now touching my wooden desk surface while typing this). The same disk in a new enclosure does not unmount at random, MacOS does not want to keep initialising it and I can boot up my Mac with the drive plugged in.
As I mentioned previously, the problem I had may be different to the issue you are facing but the problem may not be with the actual disk in the enclosure. It could be with the USB interface that the drive is connected through. I was lucky that in my case the drive had a standard SATA interface so I could connect it outside of the enclosure. I am not sure if newer drives are not directly soldered to the circuit board inside the enclosure.