Convert to Entity Query Drupal 8
You can not query file usage with entity query, it is not entity data.

You can also not do reverse joins or load specific data. Entity query gives you entity IDs, which you need to load, and then from that get the data you want.

Meaning, to do what you are doing in an enitty query, you need to build an entity query that gives you the nodes you want, then load them, then get the referenced file and then get the created value from that.