To keep in mind this Importance of this feature we at Shreeji Infosys developed this Magento 2 extension which extends the default customer registration process without affecting the default registration and provides a feature to store owner approve/disapprove every customer who register to the store. It also restricts customers from logging into website without prior approval from the store owner. This handy extension comes with all email notifications (i.e. approve, reject) to customers as well as a store owner.