Change record status: 
Project: 
Introduced in branch: 
10.3.x
Introduced in version: 
10.3.0
Description: 

JSON:API FileUpload controller uses FileUploadHandler, and no longer uses the deprecated \Drupal\jsonapi\Controller\TemporaryJsonapiFileFieldUploader. FileUploadHandler now provides common logic for file uploads in forms, REST and JSON:API modules.

Impacts: 
Module developers
Site templates, recipes and distribution developers