disable-registration
There are 3 repositories under disable-registration topic.
MagePsycho/Magento2-Store-Restriction-Pro
Magento 2 Store Restriction Pro (Restrict Access, Require Customer Approval, Disable Registration, etc.)
MagePsycho/magento2-disable-customer-registration
Magento 2 Disable Customer Registration
MaxMage/disable-registration
The extension allows you to disable customer registration in your Magento 2 store. Very Useful feature for a B2B store.