Make sure you go through all methods and wisely choose anyone to Stop or Prevent Spam Registrations in Magento 2.
Method 1: Captcha in Magento 2
Mainly, the captcha is used to detect the difference between spambots and human beings. Basically, bots are unable to solve the images task and will not be able to register. Hence, implement the captcha functionality in your Magento 2 store by applying the below steps.
Open the admin panel of your Magento 2 store and Navigate to Stores > Configuration > Customers > Customer Configuration > CAPTCHA > Forms and enable the feature as shown in the screenshot below.
Most probably, using the modern programming tactics the captcha can be sidestepped effortlessly. The best practice is using an advanced captcha. I suggest to you using any of the below captchas for advanced security to Stop or Prevent Spam Registrations in Magento 2.
Source: https://magecomp.com/blog/stop-or-prevent-spam-registrations-magento-2/