I wanted to get a shader in 1.16.4, but in Minecraft I don't have the shader settings to activate the shader. What can I do?
To do this, load Optifine (https://optifine.net/downloads).
As far as I know, there's no shader option in normal Minecraft.
Thanks but does it cost money?
No, only an Optifine cape costs money. But this is not necessary.
Got it now. What should I do?
You need Java (https://java.com/de/) and possibly "Jarfix" (http://johann.loefflmann.net/en/software/jarfix/index.html#Download)