I am not a software dev. I have noticed that it takes a long time (sometimes even months) for new apps to release a "dark mode" theme. Just curious if it was a tedious task for the devs. Isn't there an option to invert only selected elements of the app (such as the background, text grow a garden, etc.) and be done with it? I know it is a very naive approach. I would like to know the processes involved in it.

Thanks!