External Hard Drive Woes (Mac user)

[Magnum Valentino]

I've spent most of the last momth tidying up my external hard drive, an old WD Passport, 2TB storage. Mostly this involved renaming files, muxing in subs or commentary tracks, that sort of thing, using MKVToolNix. I noticed a few days ago that toolnix stopped responding while working on certain files, after hundreds upon hundred of manual jobs I ran. I presumed it was just those files, so went through the usual procedure of rebooting the computer, scanning the drive through first aid etc. There's still some spare 'safety space' on the drive, though I read this isn't really a concern with drives used only for storage.

Anyway, the problem is this -  This whole task was undertaken as preparation for backing the drive's contents up to Google Drive (thread to follow!). Now, while I can plug the drive into my TV and watch its contents as normal with no issues, when I plug it into my Mac the 'loading' screen never populates and I can't get any files off it.

For this to have happened as I loaded my very last batch of files on there is genuinely upsetting as I've spent untold joyless hours on this project this month and now I'm worried it'll all be for nothing.

Any suggestions for software or anything I might avail of to get the drive back to where it was? I'm wondering is there a 'problem file' on there somewhere that disk utility isn't able to pinpoint.