Can not open a photo library on an external drive even though it opens when copied to hard drive

Is there any way to fix not being able to open a photo library located on an external drive?

I bought a SeaGate 4TB External Drive because I was running out of storage on my MacBook Pro and found out that it was possible to place my photo library in an external drive and so free up space. I followed the instructions given by Apple, and then tried the same for my iPhone backups, and it was all working out until I took the External memory out and tried placing it back in to test if it was successful.

Well, it didn't work out; whenever I opened the Photos app a message popped up saying repair was needed to open the photo library, but even as I clicked on accept, it kept asking the same thing over and over again and the progress bar wasn't moving from the 0%. I tried erasing it and formatting it in another format, but nothing seems to work, I even tried erasing it from another Mac to see if maybe it was due to something happening to Disk Utilities.

I don't know what to do, I'm desperate since I spent 5 hours working on it and everything went to the garbage because of this, and since I spent 200 bucks on the external memory, I really need it to get working