In my opinion, creating a custom table for this case would be too complicated and it’s not related to ACF anymore. Instead, I think you can create a group field where users can save the temporary data and you can create a front end from for that field group.
You can also create a true/false field for each field for the admin to approve the data. Then you can use the acf/save_post hook to check if the admin approved the data or not. If he did, then the code will automatically update the real data by using the update_user_meta() function.
I hope this makes sense 🙂
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