I think it will be about the battle in the north during the war of the ring, I mean it's lord of the rings after all, not silmarilon or something or anything before that.
Apparently its the time between Hobbit and LOTR. Also, supposedly they are gonna milk 5 seasons... Out of a time period that Tolkien wrote bearly anything about. Also, due to legal issuses I believe they can only use events and characters mentioned in the hobbit, or invent new characters of their own (like Shadow of Mordor or Shadow of War)
Also I bet frodo will be trans vegan and the black elves will play a part too, gandalf will probably be played by a female. Thats how series are shown nowadays because people get triggered.