Xiaomi is testing a new feature that it is calling MIUI Pure Mode. Supposedly, the mode protects dangerous apps from being installed by disabling APK sideloading and background app installs. MIUI Pure Mode will be an optional feature.
https://www.notebookcheck.net/Xiaomi-tests-MIUI-Pure-Mode-to-protect-smartphones-from-dangerous-apps.558953.0.html