Recently installed shaders w/ Optifine. At first I installed an older version of Optifine, and it worked fine but I wasn't able to access my friends multiplayer server since I was playing on an older client so I installed the latest version of Optifine.
Since then shaders haven't worked at all. If I go to options, I still see an option for shaders, but it's blanked out, not allowing me to press it.
I'm assuming that you want to play on 1.15.2? Try using the latest preview version of Optifine for 1.15.2, as previous builds did not support shaders (and therefore, the button for shaders was disabled).