Well I believe that when adapting a book into a series, maybe after the first 2 seasons, the makers of the series tend to drastically implement their own ideas and plots into the movie, in order to surprise viewers who've read the book and keep the show interesting. A Classic Example is GOT (Game of Thrones). The Bienoff Brothers, followed the book by George RR Martin, probably for the first 3 or 4 seasons, and then later, started to add their own elements, gradually ending the show in a manner totally different from what RR Martin had in mind. Thought there still would be some elements of the book while adapting it into movie picture, Creative differences were major. The same can be said for Harry potter.
We should understand that reading a book and watching a movie/OTT-Series are two different experiences. The perceiving process is different. While reading, the reader imagines a world and the characters in it as one reads the written words. And in the latter, the viewer is given fixed definitions to images and character, induced and understood by the maker of the movie, and based on one's convictions of universal appeal. Sometimes these images may fall short of the descriptive imagery in the book. Sometimes the spectacle created becomes more effective than the written words. So it varies, from reader to viewer, and from filmmaker to wordsmith.
Super. Thanks for your thoughts Sir 🙏 What works for me is reading a good book, making a journey with the characters, living and empathizing with their world and imagining/thinking. And if the book is very good and has an impact, I do look out for movies/series
made on them(if any). I cannot think it will work other way around- movie first and then read a book. Very few rare cases in my opinion- Baahubali, GOT comes to my mind :)