I can’t reference an image in Next.js

From Next.js v11 onwards, you can do what you were doing without any additional config:

import macbookIphone from '../../assets/images/mac-iphone.jpg';

<Image src={macbookIphone} />

// or

<img src={macbookIphone.src} />

Ref: next/image

For earlier versions if you wish to import images instead of putting them in public directory, then you can configure file-loader or url-loader.