Coming over from eslint/eslint#17656 (comment): right now, eslintrc validates options and then validates defaults. Copying the example from @mdjermanovic's comment, if this is a rule:

{
    meta: {
        defaultOptions: [{
            foo: 42
        }],
        schema: [{
            type: "object",
            maxProperties: 2 // allows one or two in addition to "foo"?
        }]
    },
    create() {
        return {};
    }
}

...then the configuration ["error", { bar: 6, baz: 7 }] is still considered valid.

This is different from the new ESLint flat config format.

Technically this proposed stricter behavior could be considered a breaking change and out of scope given this package's feature freeze. However, I'd propose we consider it a bugfix, as IMO the invalid options should not have been allowed to begin with.

Filing a tracking issue for my reference. I plan on sending a PR for this soon, unless directed otherwise.