Help! My Lightroom backups stored on an external hard drive will no longer open!

Hi all!

I've been storing all of my Lightroom (classic) files on an external LaCie hard drive and I've never had a problem until today. I'll try to explain this neatly... my hard drive is connected to my Mac and I'm attempting to open any of my old catalogs. I'm getting the attached image over and over again while I try to open catalogs. And at other times, it tells me it just cannot open due to an unexpected error. Other times, I can open a catalog but the 'files cannot be found'. I haven't changed the locations of anything, at least not knowingly, so I'm confused (and freaking out!) why this is happening all of the sudden.

Can anyone help me troubleshoot?!