Select a shader keyword from a shader, material or renderer. (Requires Unity 2021.2+)

Parameters:

• [Optional] string name: the target. Be a property or a callback that returns a shader, material or renderer. When omitted, it will try to get the Renderer component from the current component.
• [Optional] int index=0: which material index to use when the target is a Renderer.

[ShaderKeyword] public string shaderKeywordString;
[ShaderKeyword(0)] public string shaderKeywordIndex;

[Separator("By Target")]
[GetComponent] public Renderer targetRenderer;

[ShaderKeyword(nameof(targetRenderer))] public string shaderKeywordRenderer;

private Material GetMat() => targetRenderer.sharedMaterial;
[ShaderKeyword(nameof(GetMat))] public string shaderKeywordMat;

private Shader GetShader() => targetRenderer.sharedMaterial.shader;
[ShaderKeyword(nameof(GetShader))] public string shaderKeywordShader;

It works with ShowInInspector

[ShowInInspector, ShaderKeyword]
private string ShowShaderKeywordString
{
    get => shaderKeywordString;
    set => shaderKeywordString = value;
}

It works with ShowInInspector/Button parameters & return value

[ShowInInspector]
[ShaderParam]
private string ShowShaderParam([ShaderParam] string shaderS) => shaderS;

[Button]
[ShaderParam]
private string ShowShaderParam([ShaderParam] string shaderS) => shaderS;