As of today (20190809) are Skyboxes still the only way to do a starfield background for a 3D space travel/trader game?
answer is …it depends, but yes, most games still use sky boxes, sky-spheres, or some kind of background to fill in screen space.
Then combine that with other layered effects, possibly such as large decals for nebulae, particle fx for dust with trails, to show your ship’s/camera’s direction of movement, models for planets, suns, rings, asteroids etc…
Then combine nice lighting model to light the geometry models, plus some lens flares perhaps.
Check out videos of Elite, and star citizen on you tube.