There is an option to add users to a Level when they join a site using a non-WishList Member method.
It is named “Automatically Add non-WishList Member User Registrations to this Level”
In most cases, members will gain access to Level(s) by registering using a WishList Member method. But, there are some cases where you may want to add users to a Level if they join using the WordPress registration option or using a 3rd party plugin installed on the site.
Enabling this option will automatically add the user to the Level if they join through a non-WishList Member registration option on the site.
Please note, the user must join using a method on the WordPress site. Registration needs to happen on the WordPress site for this to function.