As part of a larger work project, I needed to expose data from ACF fields the the Wordpress REST API, so I built this plugin that does this programmatically. It's 'set and forget', meaning once it's installed all existing fields and data will be exposed to the API, and any new fields and data will appear without any further setup.
The whole plugin is super lightweight, just 43 lines of PHP, coming in at just 4KB (zipped).