Software setting

E_yanks wrote:

I actually did not backup

Please describe the sequence that was used. How did the Mac get into the state where you believe it erased?

If the macOS boot-device storage was erased and if there are no backups, then...

If this is both a hard disk drive and the data was not encrypted (and if there are no backups), you can pay for recovery software or for a recovery service, amd that might recover some of the data that was here.

If this is an SSD or if the SSD or hard disk drive data was encrypted (and if there are no backups), then the data is gone and this will then next involve installing macOS as if this were a new Mac. How to reinstall macOS from macOS Recovery - Apple Support

Restore your backup.

E_yanks wrote:

Ok but please how?

Ah. I did not mean that you necessarily need to boot up from an external drive.

What I meant is that I did not think it was possible to delete essential System software from the currently active startup drive. It would be analogous to doing brain surgery on yourself.

I thought that you would have to boot from something like an external recovery disk, or a System installed on different partition on the internal drive.

At any rate, MrHoffman's advice seems like your best bet. Read that whole thing carefully to decide which option will save your documents.

I too am curious about how this happened, and/or what makes you think it did happen.

If you have (or can borrow) another Mac to create it on, I think you could make a bootable installer on a flash drive or something, and that would let you mount the internal drive, and then you can inspect it to see what can be recovered.

I think.

Maybe.

I've never had that happen to me.

If it doesn't work, then at least it does no harm.

How is it even possible, unless you booted from an external device?

John Rose6 wrote:

If you have (or can borrow) another Mac to create it on, I think you could make a bootable installer on a flash drive or something, and that would let you mount the internal drive, and then you can inspect it to see what can be recovered.

Correct. Booting from an external macOS installation will allow a look at the internal storage and if there’s anything left, yes, as will booting the Mac into Target Disk Mode and using a cable to connect to another Mac. Target Disk Mode makes the Mac into what amounts to an external storage device to the other Mac.