Actually, I don’t really understand why you want to generate the fields based on the posts. Could you please explain it to me again? I think if you have a lot of posts in the future, it will make the backend looks messy. If you still want to do it, don’t forget to update your server’s max_vars variable so all of the values can be saved. This page should give you more idea about it: https://www.advancedcustomfields.com/resources/limit-number-fields/.
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