Yep, that’s totally normal. When you enable WordPress Multisite, it automatically creates the /wp-signup.php page for user registrations across the network. It’s not from any plugin—it’s baked into how multisite works. The link on the login form to this signup page is just part of the default multisite setup.
If you want to disable it, you can customize the registration settings or even hide the link with a little CSS or custom code, but otherwise, it’s standard multisite behavior.
