Issue moving photo library

I am hoping someone might be able to help

A while back I moved my photo library from my Mac to an external SSD to save space. I don't use the photos app on the Mac much (actually very little).

I think I may have made a mistake as I was using the same SSD as a time machine target.

Today I tried opening the photo library from the SSD and Photos is saying that there isn't enough disk space to open it - I am assuming it is due to the Internal disk not having the space - but that is why I want it on an external.

I read somewhere that it won't open if it is on the same device as a time machine. So I have attached another external drive, formatted to APFS and tried to copy the library to that. However - about half way though the copy it throws up an error saying that it can't copy the file - error

"You can't copy 'Photos Library.photolibrary' because it has the same name as another item on the destination volume, and that volume doesn't distinguish between upper - and lowercase letters in filenames."

I'm a little stuck now as I'd like to point the time machine to a different drive (which has already completed a couple of good backups) - format the SSD and use that for the photo library. But I can't format the SSD until I've moved the library.