Age Of Empires: 2 Definitive Edition Tampering Detected Fixed

Add the entire AoE2:DE folder to your antivirus exclusions list.
Default path:
C:\Program Files (x86)\Steam\steamapps\common\AoE2DE

Uninstall the game, delete all leftover folders in Documents/My Games/AoE2DE and AppData/Local/AoE2DE, then reinstall. age of empires 2 definitive edition tampering detected fixed

If none of the above works, the issue is likely a background process. Perform a Clean Boot: Add the entire AoE2:DE folder to your antivirus