Automatically fill a single text column in Lists by the value of a Person Field column

Femke11 If you just want to show the email address in the list view, you can easily do it using JSON formatting like: 

{
   "$schema": "https://developer.microsoft.com/json-schemas/sp/v2/column-formatting.schema.json",
   "elmType": "div",
   "txtContent": "[$PersonGroupCol.email]"
}

Where PersonGroupCol is internal name of person or group field. You can get the internal name of your person or group column by following this article: How to find the Internal name of columns in SharePoint Online?

You can read more information about this approach in my answer given at: Get Email from user and enter into SharePoint list field 

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