Sorry about your experience, here are the solutions to fix your unreadable WD hard drive without data loss. Some of them will cause data loss, to avoid this and protect your two decades' data, sincerely suggest downloading iBoysoft Data Recovery for Mac to get your files off the hard drive first.
- Check it on another computer and reinsert the drive.
- Update the driver. Update your Mac operating system to update your driver. Apple > System Settings > General > Software Update, check for it. (Or you can visit WD's official website to see if it offers any driver updates)
- Repair the hard drive with Disk Utility. Finder > Applications > Utilities > Disk Utility, select your external drive in the left sidebar then click First Aid at the top menu bar, and then choose Run.
- Repair your WD drive with the Mac Terminal. Finder > Applications > Utilities > Terminal, type diskutil list then Enter, and type diskutil verifyDisk /dev/disk identifier to repair, finally type y then press Enter.
If these steps can't work, it's sad you have to reformat it, remember to recover and backup data with iBoysoft Data Recovery for Mac and reformat it.
Also read: How to Format an External Hard Drive on Mac?
