Starting from .NET Core 2.0 and later, the project.json file was replaced with the .csproj file format for handling project configurations. The .csproj file is an XML-based project file that contains information about the project's structure, dependencies, and settings.

To define the duration for which a user remains locked out after too many failed login attempts in ASP.NET Core Identity, you should set the LockoutDuration property. This property specifies the amount of time (e.g., in minutes) the user remains locked out before being allowed to attempt login again.

You would use UserManager.CreateAsync() to programmatically create a user account in ASP.NET Core Identity. This method allows you to create a new user with the provided email and other necessary information.

StaticFileMiddleware is responsible for serving static files like HTML, CSS, JavaScript, and images in an ASP.NET Core application. It helps enhance the performance of web applications by directly serving these files without invoking the application's logic.

To restrict access to static files for authenticated users, you should use the UseAuthorization middleware in combination with proper authorization policies. Configure your policy to allow access to these files only for authenticated users, ensuring that unauthorized users can't access them.

Implementing the "Password Complexity" option in ASP.NET Core Identity helps enforce strong password policies, preventing users from setting easily guessable passwords. It typically includes requirements for length, character types, and complexity to enhance security.

The role of the wwwroot directory in an ASP.NET Core application is to host static web assets, such as HTML files, images, JavaScript files, and CSS stylesheets. These assets are meant to be directly accessible by clients (e.g., web browsers) without going through server-side code. Placing static files in the wwwroot folder ensures they can be served efficiently and improves the performance of the web application.

In this scenario, the most suitable approach is "Database-First." This approach involves generating data models based on an existing database schema. Entity Framework Core provides tools like scaffolding to create models from an existing database, making it easier to work with legacy databases in your ASP.NET Core project.

The tool that became instrumental in converting configurations and dependencies during the migration from project.json to csproj was 'dotnet migrate.' It helps automate the migration process, ensuring a smoother transition for existing projects.

In ASP.NET Core Identity, the CreateAsync method of the UserManager class is used to simultaneously create a user and assign a password. This method takes a user object and a password as parameters, and it handles the user creation and password hashing in a secure way.