Scroll down and select (or Lock Screen and Security). Look for the Unknown Sources toggle. Switch it ON and confirm the warning prompt. Step 2: Download from a Verified Source
The last known version of the official YouTube app that reliably functions on Android 5.1 Lollipop is . This is the version you should search for. Any APK claiming to be a newer version than this is almost certainly incompatible. app youtube android 511 verified
For Android 5.1.1 users, the most reliable “verified” YouTube experience comes from: Scroll down and select (or Lock Screen and Security)