Literary and elevated register. You'd use
美女 (měinǚ) or
美人 (měirén) in everyday speech;
丽人 belongs to poetry, magazine titles, beauty-product copy, and historical drama. Famous classical anchor: Du Fu's poem
《丽人行》 (The Ballad of Beautiful Women) describing Yang Guifei and her sisters strolling by the Qujiang river in Tang Chang'an. The line above is its opening couplet.
