How to export custom post type with ACF to individual file with automation?

Schedule your backup with WP Cron – https://codex.wordpress.org/Function_Reference/wp_schedule_event

In the cron event, run your query for posts or CPTs and be sure to add 'numberposts' => -1, to return all.

When you loop through your posts from the resulting query, push the values to an array $data[]=$some_string_data_for_prop;

• https://www.advancedcustomfields.com/resources/get_field/
• https://developer.wordpress.org/reference/functions/get_post_meta/
• https://codex.wordpress.org/Class_Reference/WP_Post

And when you’re ready to write the data, convert the array values to a single string; $output = implode("\n", $data);

Then write the data to a file file_put_contents($filepath, $output);