Controlled Feature Rollout (CFR) is being used to test new features in the Microsoft Edge browser. The Chromium-based Microsoft Edge is using this procedure to introduce new features for testing and fix bugs or issues before they affect a large amount of users. Over time, Microsoft gradually increases the size of the control group to garner further feedback and usage statistics. This feature is used across Microsoft’s product line and is now also being used in Windows 10 Insider builds. For users who do not want to wait to have a feature enabled, you can enable it via the edge://flags screen.
Source: https://www.bleepingcomputer.com/news/microsoft/microsoft-edge-uses-controlled-feature-rollout-to-test-new-features/