Were you able to restore the site?
If you’re indeed running an older OS and Docker version, I recommend updating both before retrying the rebuild.
Were you perhaps updating a large database? If so, it’s possible that the update was still running. During the rebuild, you can periodically compare the size of the postgres_data and postgres_data_new directories. If the size of postgres_data_new keeps growing, the update is still ongoing. (You can also confirm whether the pg_upgrade command is running from the process list.)
You may ignore that cp error for now. I was able to update a test site on a standard install even with the same error. (It was caused by an upstream change so we’ll fix the image to remove the error, but it should not break the database updates unless the postgres configs were significantly modified beforehand.)