Love it or hate it, YouTube has a new UI that's rolling out
It's not a server switch as most people think - the switch is local. If you don't like the UI, usually uninstalling and reinstalling will revert it, not always though.
Anyway, if you want it to be enabled by force, here's how to do that:
Option 1: Using a GUI preferences editor such as Preferences Manager
1.) Download and open Preferences Manager
2.) Select YouTube from the list. You may need to enable "Show system apps" from the overflow menu first
3.) Select "com.google.android.libraries.innertube.pref.inner_tube_config" from the list
4.) Enter the following value, replacing the current one:
5.) Tap "Update"
6.) Force close YouTube from settings or reboot your device
Option 2: Manually
1.) Obtain or open youtube.xml from /data/data/com.google.android.youtube/shared_prefs (adb pull /data/data/com.google.android.youtube/shared_prefs/youtube.xml)
2.) Edit the file, changing the value for "com.google.android.libraries.innertube.pref.inner_tube_config" to the value from above
3.) Save and force close YouTube/reboot
Your UI should now be updated
Screenshots:
Thanks to @- Swift - for donating his shared prefs for testing
It's not a server switch as most people think - the switch is local. If you don't like the UI, usually uninstalling and reinstalling will revert it, not always though.
Anyway, if you want it to be enabled by force, here's how to do that:
Option 1: Using a GUI preferences editor such as Preferences Manager
1.) Download and open Preferences Manager
2.) Select YouTube from the list. You may need to enable "Show system apps" from the overflow menu first
3.) Select "com.google.android.libraries.innertube.pref.inner_tube_config" from the list
4.) Enter the following value, replacing the current one:
Code:
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6.) Force close YouTube from settings or reboot your device
Option 2: Manually
1.) Obtain or open youtube.xml from /data/data/com.google.android.youtube/shared_prefs (adb pull /data/data/com.google.android.youtube/shared_prefs/youtube.xml)
2.) Edit the file, changing the value for "com.google.android.libraries.innertube.pref.inner_tube_config" to the value from above
3.) Save and force close YouTube/reboot
Your UI should now be updated
Screenshots:


Thanks to @- Swift - for donating his shared prefs for testing