Hmmmmmmm (PSEUDO CODE)

idea.ts

function defineDefaultProps<Props>(defaultProps: NoInfer<Partial<Props>>) {
  return function resolveDefaultProps(props: Props): Props {
    return {
      ...defaultProps,
      ...props
    }
  }
}

interface Props {
  theme?: 'light' | 'dark';
  children?: ReactNode;
}

const resolveDefaultProps = defineDefaultProps<Props>({
  theme: 'light'
})

function Component(props: Props) {
  const propsWithDefaults = resolveDefaultProps(props)
        
  return (
    <div>
      {propsWithDefaults.children}
    </div>
  )
}

I don't like that you must break a very common eslint rule (no param reassign) if you want to keep the props name. Or you have to name the prop parameter something else lol