How to Run Code When the Block Editor Initializes (Gutenberg) https://benjaminintal.com/2020/01/26/how-to-run-code-when-the-block-editor-initializes-gutenberg/

index.js

import { registerPlugin } from '@wordpress/plugins'
import { useEffect } from '@wordpress/element'

const doSomething = () => {
  useEffect( () => {
    // Do whatever when the block editor is initialized.
  }, [] )
  return null
}

registerPlugin( 'do-something', {
  render: doSomething,
} )