https://www.bleepingcomputer.com/news/microsoft/windows-10-insider-build-17686-released-heres-whats-new/

Today Microsoft released Windows 10 Insider Preview Build 17686 (Redstone 5) to insiders in the fast and skip ahead rings. This build adds local experience, privacy, and Windows Mixed Reality improvements.

This build adds a new "Region" settings page that allows you to override various settings related to your default Region settings. For example, you can change the type of calendar you wish to use, which day is the first day of the week, and short date formats.