It seems this issue has been widely discussed. When I attempted to run Disk First Aid on “Data” from my internal drive, the process failed. I followed some advice regarding the (-69845) error: I tried running Disk Utility in Recovery Mode, but it couldn’t resolve the issue.
My question is: if I erase the Mac, reset it to factory settings, and then restore my files from Time Machine, would this resolve the issue? Or is there a better alternative you could suggest?
Hello, sorry to hear about your issue. Maybe you can try Single User Mode.
Restart your Mac and quickly press the Command and S keys then release them.
Type /sbin/fsck -fy in the Terminal window.
Repeat /sbin/fsck -fy until you see The volume appears to be OK.
Type reboot and press the Enter key.
Or you can try Disk Utility after entering into macOS Recovery Mode. Then Run the First Aid there.
Lastly, how about erasing your Mac and reinstalling macOS like you said? Please backup all the files. And both Clone or Time Machine can help you, don’t worry.