Android has become stricter with file permissions. The OBB setups will include instructions for "Scoped Storage." If the OBB doesn't place correctly (usually in Android/obb/com.square_enix.android_googleplay.FFX/ ), the game won't load.
While many other titles in the series have official mobile ports on the Google Play Store final fantasy x android apk obb best
This is a deep-dive review of on Android. Android has become stricter with file permissions