OpenGL itself isn’t supported on the web at all, so you can’t use it if you wish to run there. According to Emscripten, they support a “WebGL-friendly subset of OpenGL ES”, and they also try to emulate the unsupported features at a performance cost.
I don’t know anything about SDL3, but I know SDL2 supports Emscripten just fine, including its native 2D graphics engine. If it’s enough for you, then you can entirely ignore any OpenGL and let SDL handle it for you.