External ssd drive will not mount

I didn't format the drive on my iMac.

However, I did format the drive again on my Macbook Pro and then took my external photo drive from my iMac and connected it and my X9 Pro drive to the Macbook. Both drives showed up on Finder and Desktop. I then copied the files from my photo drive to the X9 Pro.

Next, I ejected my photo drive, leaving the X9 Pro drive mounted. I then opened a photo editing software program, pointed it towards my X9 Pro and all my images were there and I was able to access the drive, edit photos, save them back to the drive, etc.

As another test, I ejected the X9 Pro and closed down the Macbook. After a while, I opened the Macbook, logged in, connected the X9 Pro and again it showed in Finder and the Desktop. So, I guess all is fine now. Perhaps it was something going on while copying files while the external drives were mounted on my iMac? I'll be playing around with the Macbook and X9 pro drive and watch for anomalies. Currently all seems to be working as I expected.

Thank you All for your help. I appreciate you and this community.

Thanks for pointing that out to me. I hadn't noticed the no capacity. I went and got a new cable. I erased and formated the X9 Pro on the MacBook and it looked good. I connected the X9 Pro to my iMac and copied my photos to the drive. On my iMac everything looked good. The files were on the drive, the drive showed on the desktop and finder. I ejected the drive and connected it back to my MacBook.

The drive did not show up on my desktop or Finder. It did show up under Disk Utility and was unmounted!

Looking at the image below; if I were to click on "Container disk5" it tells me that the capacity is 4TB, Free is 3.63 TB and Used is 372.45GB. Then if I click on X9 Pro it reads the same as the image below.

I tried connecting to my iMac again and it doesn't show up there either!

I'm wondering if my formatting is not correct, if the drive is faulty or is it the MacBook?

It shows in Disk Utility, but says unmounted on my MacBook, but now it does the same on my iMac. It does not show on either computer's Finder.

Yes, I have.

Screen shot of Disk Utility. FYI - when I click on mount, nothing happens. However, the drive's LED shows activity or at least flashes.

No utilities shipped with the drive. I didn’t install anything.

no, I haven’t tried formatting the drive on my iMac. I will give that a shot.

Grant - sorry for the confusion. I was referring to the image that I had previously posted and then I wrote out what the other "screens" described. I didn't intend to post new screen captures.