The The Customer Approval for Magento 2 extension allows store owners to take the whole control of any new account creation at the frontend. Display a customized disapproved and pending accounts messages right at the storefront. Approve only real customers account and reject all spam accounts. Notify customer by email on account approval and rejection. Notify admin by email after each new account registration.

Check more details here: https://www.ulmod.com/customer-approval-for-magento-2.html