You could mine more material from the appendices at the end of ROTK for a movie. Stuff about the early days of Gondor including the kinstrife, and eventually the end of the line of the king in Gondor (wouldn’t mesh well with the history provided in the movie ROTK tho). Also, the invasion of the wainriders, and the first ride of the Rohirrim from the far north, past Lothlorien, to come to come to Gondor’s rescue and be given the land of Rohan for their own.
Heck, the fall of Minas Ithil and its transformation into Minas Morgul, along with Minas Anor becoming Minas Tirith would be an interesting story.
Aragorn’s early days, including his adventures as Thorongil, warrior of Gondor and favorite of Ecthelion, Steward of Gondor and envy of Denethor would also be interesting. It included side trips to Rohan along with adventures alongside Eomund, Eomer’s dad.
Also, Gandalf and Aragorn’s hunt for Gollum, his eventual capture and imprisonment by the elves, and subsequent escape would be of interest.
One could make a movie out of the adventures of King Dain Ironfoot and King Brand son of Bain son of Bard of Dale, fighting in the War of the Ring, to prevent the destruction of their kingdoms.
Saruman’s fall, including his forging of his own rings, his hunt for the One Ring, and his first use of the palantir could be used also.
Lotsa stuff could be expanded into a movie adventure without having to touch the Silmarillion, UT, or HOMES.
Note I say that it could be done, not that it should be done.