Internal disk has disappeared

It can be a real disk issue.

In DiskUtility, first do FirstAid several times; Then try to format it (Partition tab next to FirstAid tab):

GUID partition table, APFS (just APFS, not anything else).

If that should succeed try installing again.

drstevea wrote:

Thanks for the suggestion, Lexiepex. I tried it: ran FirstAid three times, then partitioned the disk. That seemed to work OK. Then I tried reinstalling macOS in the new partition. The installation ran a lot longer than it has on previous tries, and I was feeling optimistic, but then I got the "installation couldn't be completed" message again.

I just had a laptop which had similar issues. While I was able to reinstall, I believe the SSD or Logic Board has a problem.

I send the whole installation log to Apple and asked them what to do, but they haven't answered from the last log I sent in several days ago. Do they answer on those messages?

No, Apple does not respond. They just use those logs to try and fix thing in future updates.

"Do they answer on those messages?" Depending where you have sent it, I guess.

So it is a bit better but not completely.

A very good and documented info app about disks is DriveDx you can download it here:

binaryfruit.com

Do not download from the Appstore because that version will not check external disks, and it is not free.

DriveDx gives very detailed information on disks and what is good what is wrong.

Download it and use it, read the explanations on the information by hovering the mouse over it.

The first 10 (or so) runs are free.

It sounds like you may have a hardware issue. You should take the laptop to Apple or an Apple Authorized Service Provider to be examined.

In Disk Utility click "View" and select "Show all devices". If you do not see the physical SSD in the left pane of Disk Utility then your SSD has died and will need to be replaced.