https://wccftech.com/how-to-recover-files-lost-windows-10-1809-installation/

Several users have reported losing their files, documents, and installed programs after installing Windows 10 1809. While this isn’t happening to everyone and could be avoided through a full backup, the problem is certainly a serious one. Microsoft has confirmed that the company is “actively investigating” the problem. But if you have already lost your data in the excitement of a new Windows 10 version, you can easily recover the lost files.

Since the upgrade process has only deleted and not moved the files, they are easily recoverable using a recovery tool. Some users have reported (via SW) using Recuva for the process and have successfully retrieved all their data. You can download the free version of Recuva from CCleaner and restore your lost files. But you can use any other recovery tool for the process too; just make sure not to do anything before running the recovery tool to ensure you restore all your deleted files.