Android 5.1.1 (Lollipop), released in 2015, is considered a legacy operating system. While it powered iconic phones like the Samsung Galaxy S5 and Nexus 5, it has not received official security updates from Google for several years.
If you choose to use an older APK, the following were the last major versions to support the Lollipop API (API 21): Official YouTube 16.40.36 youtube apk android 511
If you are using a legacy device, you have three primary options for accessing content: Keeping YouTube Alive on Android 5
Since the official APK is unreliable, most enthusiasts and reviewers recommend these third-party clients: released in 2015
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