The user's profile was deleted in outlook, as a result of which the corresponding OST file was deleted.
Why this happened is unclear and does not matter now. I have repeatedly tested deleting the profile and the OST file is not deleted.
Subsequently, the deleted OST file was recovered by disk utilities, but turned out to be corrupted.
Most of the utilities could not recognize the structure of the outlook file in the file.
The utility scanned the file for metadata and restored part of the data, except of course those that were required ("notes").
I need to restore "Notes".
Maybe someone faced a similar problem. I would appreciate any help.