Go to your phone settings and allow installations from your browser or file manager.
The most reliable and safe way to experience authentic ETS2 on your Android device is by the official PC game. Shadow.tech Safe Ways to Play on Android
Since there is no official OBB or APK for the original game, many players use dedicated mobile truck simulators that offer similar gameplay: Truckers of Europe 3
on Android often leads to websites claiming to offer a mobile version of the game. However, it is important to know the actual status of the game: The "Patched" Android Version Reality
