The absolute final official version of the main YouTube app that supports Android 6.0.1 is .

This guide explains the current state of YouTube compatibility for Android 6.0.1, how to safely find the correct APK, and alternative ways to stream content on older hardware. The Reality of YouTube Support on Android 6.0.1

Here is what a "ReVanced" experience can offer, without a paid subscription:

Please note that downloading and installing APK files from third-party sources may pose security risks. Be cautious when downloading and installing APK files, and ensure you have a reliable antivirus software installed on your device.