How do I install Minecraft shaders?

I installed Optifine for the latest Minecraft version 1.15.2 and wanted to take a look at InGame in the settings and then I noticed that I can't click the "Shader" button (it is greyed out). For others who have also installed Optifine, they can click the Shader button despite the fact that they have no shaders installed.

Can someone help me.

Here is a tutorial.