Not a ton, which is a real shame because I adore 'Wonder'. Wonder's author, R.J. Palacio, has basically spent years building on that universe. There's 'Auggie & Me', which is three stories from Julian, Christopher, and Charlotte's points of view. It's not a sequel exactly, more like companion pieces that flesh out the world.
She also wrote 'White Bird', which is a graphic novel about Julian's grandmother's experience as a Jewish girl hidden in Nazi-occupied France during World War II. It connects back to Julian's character arc about redemption. It's interesting, but tonally it's a much heavier historical piece compared to the middle-grade contemporary feel of 'Wonder'.
Beyond that, I think there's a picture book called 'We're All Wonders' for younger kids, adapting the message. Her bibliography feels very focused, like she found this profound core idea with 'Wonder' and has been exploring all its facets and echoes through different formats and character lenses, rather than jumping to a completely new standalone story. It makes her work feel cohesive, even if I sometimes wish for a brand new cast from her.