YouTube introduced one dark mode for his desktop app last year, and then rolled it out for iOS users in March of this year. In July, Google announced that Android users could switch from the usual white background on YouTube to the new dark theme, but that seems to have been a very limited roll out.
However, after waiting for months, all Android users can finally turn on dark mode on their mobile apps. Some Redditors spotted that the latest version of the Android YouTube app, version 13.35.51, will be rolled out further with the option to enable dark mode.
To enable YouTube's dark mode on your Android device, open the app, go to the settings window, and tap General. You see the toggle switch to turn on the dark theme.
However, if you can not see the option, 9to5Google suggests removing the app from the Recent menu and restarting it to activate the update. If that does not work, you can try to update it through Google Play or sideload the installer APK Mirror.
If you have already set it up, welcome the dark side.