How do I disable the underlining of Rust variables and their methods in Visual Studio Code?

The underline is intended to draw attention to mutable variables and methods. It can be disabled by adding the following to your settings.json:

{
    "editor.semanticTokenColorCustomizations": {
        "enabled": true,
        "rules": {
            "*.mutable": {
                "underline": false,
            }
        }
    }
}