Here is the critical takeaway: You are not a cheater. The error is triggered by legitimate software or corrupted updates.

Navigate to your Steam user data folder: C:\Program Files (x86)\Steam\userdata\

How to Fix the "Tampering Detected" Error in Age of Empires 2: Definitive Edition

If you play via the Xbox App, outdated Windows Gaming Services can trigger authentication errors. Similarly, missing system files can cause processing errors.