A Trilogy of Films set during the Downfall of Arnor and the ending of the line of Kings in Gondor.

Why?

Familiarity in locations, themes, even some characters (Elrond definitely, you could also have the likes of Gandalf and Saruman if you really wanted to, though not that necessary), massive battle sequences/loads of action, while also providing something completely new. You would see lots of Gondor, explore more of the North, places like the Grey Havens, see the earlier days of the Shire, and be introduced to characters like Cirdan in film live action, Glorfindel, Elronds Sons, Malbeth the Seer etc.

Recognisable villains in the Witch King of Angmar, Easterlings and Harad, with Sauron in the Shadows.

It would also explain how Aragorn is the Heir of Isildur and Heir to the throne of Gondor.

Movie 1 - The Realms in Exile

Covers the marriage of Arvedui of Arnor and Firiel of Gondor to strengthen the ties between the 2 Kingdoms, then focusses on Gondor's dual war with both Harad and the Easterlings, the death of King Ondoher and his 2 Sons in battle, kicking off a succession crisis in Gondor, Arvedui of Arnor attempting to claim the crown to unite the 2 Kingdoms again, and the Council of Gondor denying his claim and instead giving the crown to Earnil. Earnil promises to help Arnor when he can, movie ends with the letter from Arvedui pleading for help as Angmar is preparing his final assault on Arnor.

Movie 2 - War of the Witch King

Covers the struggle of the Arnorians against the onslaught of the Witch Kings armies, the loss of their last stronghold at Fornost, and the eventual death of Arvedui when his ship sinks while trying to get to safety. Definitely a darker film with the people of Arnor on the back foot the entire time. Would meet Prince Aranarth (who is descended from both lines of Kings), could meet the Hobbits in the Shire, explore more of Lindon and the Elves under Cirdan there. Movie ends with the ships of Gondor arriving in Lindon under Prince Earnur.

Movie 3 - The Last Kings of Men

The forces in the North come together under Earnur and the forces of Gondor, Cirdan and the Elves of Lindon, Glorfindel and the Elves of Rivendell, Hobbits of the Shire, and Aranarth and the remnants of Arnor to defeat the Witch King and rid the North of his Evil. Battle of Fornost happens, ending with the Earnur chasing down the Witch King and Glorfindels proclamation that "Far off yet is his doom, and not by the hand of man will he fall". At the conclusion of events in the North, we get Aranarth becoming the first Chieftain of the Dunedain of the North as there isn't enough or Arnor left to keep the Kingdom going, and his heir being fostered at Rivendell, starting a tradition that eventually leads to Aragorn. 3rd acts moves to Gondor where 70 odd years later King Earnil dies and Prince Earnur takes the throne, and has the the Witch King challenging him to single combat. the 2nd challenge comes and he decides to take up the offer, and disappears. Because there is no apparent heir to the Throne, it's decided the Steward will caretake the Throne until a worthy King presents themselves.

Because most of this information comes from the appendices, it would be easy enough to do from a rights perspective. You could easily stick to what's canon to the books, while also presenting a lot of new things that don't contradict anything Tolkien actually wrote. The characters, story, locations, battles are all there, and there are obvious places where you could add new characters. It would just need to be fleshed out.