If sideloading fails, you can always watch YouTube through a modern browser:
The v17.39.46 APK will likely work for another 6–12 months. However, as YouTube’s backend changes, even old APKs may eventually stop playing videos. For the best experience, consider: youtube apk android 6.0 1
Use your browser to download the YouTube 17.34.36 APK. Open your File Manager (or "Downloads" folder) to find the file. If sideloading fails, you can always watch YouTube
For Android 6.0, you should look for YouTube versions in the 12.x to 14.x range (e.g., YouTube v14.21.170). If sideloading fails