[Mithadan]

I would temper Tar Elenion's position a bit. What Tolkien published during his lifetime and did not later correct in a subsequent or corrected edition is absolutely "canon." What Tolkien wrote but did not publish? Personally, for such materials canon is in the eye of the beholder. Everyone must agree that Tolkien's mythos encompassed tales from the First and Second Ages that were never finished. What ultimately became the 1977 Silmarillion is, at best, a version of what Tolkien wrote based upon Christopher's best guess at that time. The stories were in a constant state of flux up to the time that the author passed away. From those DRAFTS we can discern the contours of what Tolkien generally intended. But not the specifics. Beren and Luthien may have reached a point where it was maybe 65% final. The Hurin/Turin stories may have reached 85% completion or more. But they were never finalized. Names might have changed. Events may have changed. The basic threads of the stories may have been set, but are they "canon?" I don't know.

In my image of Middle Earth, the world was not round at its outset (that sounds really strange to say it), there were no Domes of Varda, Orcs are corrupted Elves not Men or beasts. Yet Tolkien "wrote" versions of his tales, or at least musings about them, that differ from my preferred views. Who is to say what is "canon?" Not I. Not Peter Jackson and not Jeff Bezos.

RoP was "licensed" by the Estate. I will not bore you with anything resembling a formal legal definition of the word. To me, "licensed", as in you can use place names, characters, concepts to build your own story that you can publish as being "based upon...," is not the same as "canon." That being said, my own view of canon has shifted over the years. RoP is an interpretation, as others have suggested, a fan fiction of sorts. If you like it, watch it and enjoy. If you do not, don't watch it. I don't even mind if you want to watch it in order to point out where it deviates from your version of "canon" so long as you (not directed at anyone in particular) accept that others might disagree and choose to watch it (and discuss it) because they enjoy it and want to do so.

Otherwise, I invite anyone who would like to do so to use our (semi-functional) search function and seek references to "canon." You will get voluminous results.

EDIT: To be clear, feel free to discuss "canon" to your hearts' content. I do not mean to suggest that my post is the final word on the subject.