SDL3 added a way to tell SDL to render vertex-based geometry as well: https://wiki.libsdl.org/SDL3/SDL_RenderGeometry. Those vertexes can have 3D positions, so that counts as a 3D renderer I guess. Though of course the GPU is doing the heavy lifting; SDL is just exposing a little bit more of the GPU's functionality. It's quite useful for some 2D applications as well. I remember reading about how it could enable more efficient drawing of 2D plots or cleaner ImGUI integration, though I don't remember details.