How would I do this if I had to do it.
I would create a true false field “Add New Member”
Then I would create 3 fields Name, Slug and Description. These 3 fields would be conditional and only show if Add New Member is true, these fields would all be required.
Then I would create an acf/save_post filter https://www.advancedcustomfields.com/resources/acf-save_post/. In this filter I would
But to be honest, I would not probably do this unless I had a client that insisted on it. I would tell them that before they add a new post for a member that does not exist that first they must add the member. Or I would tell them that they will need to go to the member when they are done with adding the post and add a description for the member after the fact. This is no different than adding a category, or (product category in woocommerce), the only thing that you can do is add the name and then you need to go to that category and add a description and other information if the site needs it later.
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