Anything accessible to both client and server-side code should be under publicRuntimeConfig.
A page that relies on publicRuntimeConfig must use getInitialProps or getServerSideProps or your application must have a Custom App with getInitialProps to opt-out of Automatic Static Optimization. Runtime configuration won't be available to any page (or component in a page) without being server-side rendered.
To get access to the runtime configs in your app use next/config, like so:
 import getConfig from 'next/config'
import Image from 'next/image'
 
// Only holds serverRuntimeConfig and publicRuntimeConfig
const { serverRuntimeConfig, publicRuntimeConfig } = getConfig()
// Will only be available on the server-side
console.log(serverRuntimeConfig.mySecret)
// Will be available on both server-side and client-side
console.log(publicRuntimeConfig.staticFolder)
 
function MyImage() {
  return (
    <div>
      <Image