For Android 10 (or newer) users:
Select your profile picture . Tap Settings . Tap General. Tap Appearance. Select "Use device theme" to use your device's dark theme setting. OR Turn on Light or Dark theme within the YouTube app. For other Android users:
Select your profile picture . Tap Settings . Tap General. Turn on Light or Dark theme in the YouTube app.
YouTube Android supports dark mode. Learn more about YouTube Android on the website.