Microsoft plans to implement the new Fluent Design framework across the entire Windows 10 OS, and File Explorer appears to be the next part to get the new look. Apart from new transparent and reworked visuals, File Explorer will finally support tabbed windows and sets. This revamp is scheduled to be introduced with the 2020 major update.
https://www.notebookcheck.net/File-Explorer-to-get-Fluent-Design-revamp-with-Windows-10-April-2020-update.415092.0.html