https://www.theregister.co.uk/2019/12/16/google_android_dark_mode_scheduling/

During the heady beta days of Android 10, Google showed off a feature that would allow users to automatically activate Dark Mode depending on the time of day. Sadly, despite an enthusiastic reception, it never made it into the finished product, due to several technical hurdles.

However, according to a company representative, Google plans to bring it back in a future update of the mobile operating system.