Which SWA template application is NOT suitable when creating a custom application with Username, password, and submit button fields?

The Template Plugin App 3 Fields is not suitable for creating a custom application with Username, password, and submit button fields because it is designed for scenarios where additional fields beyond just username and password are needed. Typically, this template allows for more complex login requirements, possibly including multi-factor authentication or other user input fields that are specific to certain applications.

In contrast, the Template Basic Auth App focuses on a straightforward setup that requires only a username and password, aligning well with the typical requirements for a custom application login form. The Template Plugin App and Template Enterprise App also offer configurations that can effectively handle traditional username and password authentication without complexity. Therefore, while the other options cater adequately to standard authentication processes, the Template Plugin App 3 Fields introduces elements that exceed the basic requirement of a username, password, and a submit button, making it inappropriate for this specific use case.