https://www.techradar.com/news/microsoft-delays-the-sets-feature-for-windows-10

The upcoming Sets feature for Windows 10, which adds a web browser-like tabbed user interface for easier navigation and organisation of your apps, has been delayed by Microsoft.

An early version of the feature first appeared in Redstone 4, which was a beta testing version of the Windows 10 April 2018 Update, but it was removed from the final release.