Microsoft introduced the Tamper protection feature in Microsoft Defender ATP earlier this year. It is a new setting to protect against changes to key security features, including limiting changes that are not made directly through the app.
Initially, Microsoft made the feature available only for Windows Insiders and continues testing the feature. The feature was available to Windows Insiders since December 2018.
In March 2019, Microsoft rolled out the full functionality of the feature to Windows Insiders and continues working on the feature.