The Silmarillion is a very loose narrative of the First Age from Creation (my favorite thing Tolkien ever wrote is the Ainulindale) to fall of Beleriand. It then has a few brief glimpses of the second age and the forging of the Rings. But, honestly, the Two Towers and Return of the King are just...moving. I think you’d get more out of The Silmarillion afterwards. The Fall of Gondolin and Beren and Luthien (both now further fleshed out in books) are top tier Tolkien so you can’t go wrong reading it. But it’s far more expansive than the intense closeness of the trilogy.