ACF attachment custom field in rest response

Check out ACF to REST API – https://github.com/airesvsg/acf-to-rest-api

You can optionally turn on/off which fields you want to enable.

// Enable the option show in rest
add_filter( 'acf/rest_api/field_settings/show_in_rest', '__return_true' );

// Enable the option edit in rest
add_filter( 'acf/rest_api/field_settings/edit_in_rest', '__return_true' );