How to Enable Dark Mode on YouTube on iOS
If you’d like to use YouTube Dark Mode in the YouTube app on an iPhone or an iPad (iOS 13 or higher), here is what you need to do: Click on your account picture in the top-right corner of the app. Then, Choose Settings > General > Appearance. Here, you can choose between Dark Theme, Light Theme, or Use device theme. Selecting ‘Dark Theme’ will enable it as your default view. If you select ‘Use device theme’, your YouTube background will depend on your device's dark theme setting. If you change your mind, follow the same steps to revert to a light theme.