SDL2 and SDL3 both have hardware accelerated 2D renderers, appropriately called SDL_Renderer. You can tell SDL to upload pixel buffers to GPU textures and tell SDL to draw those textures on the screen with various transformations and color effects.
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.
SDL_RenderGeometry(Raw) are only capable of 2D rendering and the vertexes do not even have a z-coordinate.
Genuine 3D support is available in SDL3 via the GPU types and functions: https://wiki.libsdl.org/SDL3/CategoryGPU
If you want to get pedantic the hardware rasterizer in your GPU doesn't rasterize "3D triangles" either. Any notion of '3D' comes from how you project your vertices when transforming them through your coordinate spaces. Though the perspective divide needed to make perspective projection work is baked in, but otherwise NDC is a 2D space. Z only exists for the depth buffer/depth test and perspective correct interpolation. The "shape" of the triangle on screen isn't affected by it.
As long as you can draw 2D triangles there's nothing stopping you from drawing a "3D" scene with a software transform pipeline. Depth sorting gets fun without a z-buffer though.
Except perspective correct interpolation isn't something you get to disregard in a footnote.
Oh, I stand corrected. Thanks!