Below is an excerpt from another post that explains how I believe user specific columns work. I believe the values are stored in a separate hidden glide table. Not directly in the table that contains the user specific column…although it may visually appear that way and you can work with it like it is. I think it’s just a special type of relation with direct access to the value in that hidden table.
If you want to periodically access user specific data, you can manually export the app data as a CSV file that’s emailed to you.