I've not seen Rings of Power yet, but it will be set in the Second Age because, well, that's when the Rings of Power were created. A relatively affluent and peaceful time for Middle Earth (in comparison to the Third Age) for a while and there should be plenty of background material on which to base the storyline. Tolkien left huge quantities of notes and so forth which is why his son has been able to publish so many flipping books about Middle Earth! My guess it will be about the forging of the rings so I expect to see lots of Elves, a bit of intrigue and Sauron being a bit naughty. It will finish in a very large battle where most of the good guys die.
I also predict some pretty witless dialogue at times if the LoTR and Hobbit movies are any indication! Oh, I suspect there will probably be some Elves who look old, for some unexplained reason...