I do not know if it is ok for everyone on the dark version than on the light, but since Apple has launched "dark mode"On macOS Mojave and newer, on iPhone si iPad, with iOS 13 / iPadOS 13, I use this "dark" interface and I would never go back to the light version. First of all, in low light, at night, the dark interface is better for reading and better highlighting the images. For no reason photos use websites with black background or dark gray shades.
After which Apple they started with "dark mode", many websites and iOS applications have been adapted to be used in "dark mode", either automatically, if iOS is set to this mode or left to the user's own choice.
Facebook company was not far behind and earlier this month launched "dark mode" for Instagram. A wise decision, especially since Instagram is based on images, and as I said earlier, the black highlights the details. It's about contrast.
Recently, some users have been testing "dark mode" for the Facebook web interface, followed shortly by those who use Facebook on Android. By the end of this year, Facebook is expected to receive the dark interface for both the web version and iOS and iOS applications. Android.
It is unknown why Facebook did not leave "dark mode" for all users, but most likely it is tests, before the official launch for all. This was done before the profile picture went from the square on the left side of the profile, to the round profile image on the center of the page.