If you need a custom login page created in mendix studio pro, you have to allow anonymous user. and give him the right to access that login page only (and set it as his default home page in the navigation)

Create a Custom Login Page: First, create a custom login page in your Mendix application. Design and configure this page according to your requirements. Ensure it has the necessary input fields for username and password entry.

Create a Microflow for Login Logic: Create a microflow that will handle the login logic. This microflow will validate the user's credentials and perform the login action. Inside this microflow, you can use the Login action to authenticate the user. You can add your custom logic for handling authentication and authorization before using the Login action.

Disable Anonymous User Role: In the Mendix Security settings, disable the "Allow anonymous users" option. This ensures that users must log in before accessing any part of the application.

Set Up Navigation: Configure your navigation to start with the custom login page. In the Navigation settings, set the "Home" page to be your custom login page.

@Sahil Pathina, Even I have same kind of requirement, where the admin will create the credentials for the user, they have to login with the credentials provided by an Admin. Here the problem is, I have username and password fields, but the problem was once, In login page how should I capture those User Id and password in different page.I don't have those details while doing validation right ?  I was creating the Non persistent entity to capture those details and I had mapped those details to the data view in Login page. Now when navigating to this page through a microflow call, I was getting an issue. Error was something like, arguments were not available from navigation.