Create a new user on Webform submission
You can write your own WebformHandler to do so. Just extend WebformHandlerBase and write your code into the postSave() function. Here is a little example: https://gist.github.com/mharmuth/0ab021d5b65e4cab7c6efec951fc59e9

This class has to be stored in your custom module in the directory your_custom_module/src/Plugin/WebformHanlder/CreateUserHandler.php

After creating this handler, you will be able to add it in your webform under "Email/Handlers".

Hope this helps ;)