I can’t save my database.
Make a folder for backups in C drive and save there.
You have to change user security settings for %Users% folders.
search for NT Service\MSSQL on forum.
Swl service does not have permissions for that folder.
I had the same problem with a customer 3 days ago. I saw that the problem was caused by Avast antivirus application. When I disable antivirus application, it backed up smoothly.
Thank you 