"File system verify or repair failed. :(-69845)" occurs when running First Aid to repair an external disk, such as a Time Machine disk or an EXFAT disk. It likely roots in file system corruption on the drive, which can be caused by sudden power failure, catalog file corruption, invalid volume header, virus attacks, etc.
To fix File system verify or repair failed. :(-69845), there are different solutions for the external and internal hard drives.
For external hard drives:
For internal hard drives:
You can fix the "File system verify or repair failed" error with a handful of tools built into Mac. But certain solutions like reformatting drives will have your data erased. If you don't have any backup, you can use iBoysoft Data Recovery for Mac to recover your data from corrupted drives before you format them.