Here's an ellipsoid in build123d using geometric transformation of a sphere:

    from build123d import *
    mat = Matrix([[2,0,0,0],[0,1.5,0,0],[0,0,0.5,0]])
    ellipsoid = Sphere(100).transform_geometry(mat)

Also, FYI build123d now runs in the browser thanks to OCP.wasm. Example playground here https://jojain.github.io/build123d-sandbox/