Is there a way to have mapped type together with index signatures?

Question

Consider example below

type Config<T> = {
  [K in keyof T]?: { render: (value: T[K]) => React.ReactNode };
};

type TableProps<T> = {
  data: T[];
  config: Config<T>;
};

const Table = <T,>(props: TableProps<T>) => {
  return <div>{/** */}</div>;
};

type Line = {
  name: string;
  age: number;
};

export const App = () => {
  const data = useMemo<Line[]>(() => [], []);

  return (
    <Table
      data={data}
      config={{
        age: { render: (value) => value },
        name: { render: (value) => value }
      }}
    />
  );
};

This works fine when I want to use keys of Line type for Config type. But is there a way to add other optional keys that does not belong to Line type. In the end I want the render method to know what type of value it receives upon creation of config object as a prop for Table

Case 1
As age and name are keys of Line render method knows value is string and number

      config={{
        age: { render: (value: number) => value },
        name: { render: (value: string) => value }
      }}

Case 2
I want to add properties that are not part of Line to config

      config={{
        age: { render: (value) => value },
        name: { render: (value) => value },
        randomProp: {render: (value: unknown) => /** do some transformation */}
      }}

To achieve Option 2 I need to change Config type to something else. I tried to do it like this but it doesn't work. Type for value is always unknown

type Config<T, P extends keyof T> = {
  [K in P | string]?: { render: (value: K extends keyof T ? T[K] : unknown) => React.ReactNode };
};

type TableProps<T, P extends keyof T> = {
  data: T[];
  config: Config<T, P>;
};

const Table = <T, P extends keyof T>(props: TableProps<T, P>) => {
  return <div>{/** */}</div>;
};

export const App = () => {
  const data = useMemo<Line[]>(() => [], []);

  return (
    <Table
      data={data}
      config={{
        age: { render: (value) => value },
        name: { render: (value) => value },
        randomProp: {render: (value: unknown) => /** do some transformation */}
      }}
    />
  );
};

Type '(value: number) => number' is not assignable to type '(value: unknown) => ReactNode'. Types of parameters 'value' and 'value' are incompatible. Type 'unknown' is not assignable to type 'number'.ts(2322)