Tamper Protection protects security settings for Windows Defender antivirus from being disabled by malware or third-party programs. If a program, such as malware, or even PowerShell tries to change security settings or Microsoft Defender preferences, it will block the settings from being modified. If you have non-Microsoft antivirus software installed, Microsoft will register it as your antivirus provider and disable Windows Defender. This also means that Tamper protection and other features will be disabled as well. The feature is an integral part of the Windows 10 security environment.
Source: https://www.bleepingcomputer.com/tutorials/how-to-enable-windows-10-tamper-protection-security-feature/