Some old versions of Shadersmod were said to be compatible with Optifine. That was true before Optifine has shaders features. After Optifine has its own implementation of shaders features, you can't mix the two. You can only use version that was made for specific Minecraft version anyway and there is no Shadersmod for new Minecraft version.
I no longer update this mod partly because it is not needed. You can just use Optifine for newer version minecraft without Shadersmod.
Another reason is lack of time due to other activities.