Facebook is well know social media platform. But their are many users who are facing Facebook dark mode keeps turning off issue. If you are one of the user then you can read and apply given methods:

Check your dark mode settings
Open your facebook app on your iphone
Click on your profile icon
Then tap on Settings and Privacy
Under Settings and Privacy click on dark mode
Select the turn dark mode option.

For more information: https://ityug247.com/how-to-fix-facebook-dark-mode/