❔ Entity Framework not required foreign key as required?

public class User : IdentityUser
{
    // Add additional data here
    public string DisplayName { get; set; }

    public ICollection<Bookshelf> Bookshelfs { get; } = new List<Bookshelf>();
}

public class User : IdentityUser
{
    // Add additional data here
    public string DisplayName { get; set; }

    public ICollection<Bookshelf> Bookshelfs { get; } = new List<Bookshelf>();
}

public class Genre
{
    public int Id { get; set; }
    [Required]
    public string Name { get; set; }

    public List<UserGenre> UserGenres { get; } = new();
}

public class Genre
{
    public int Id { get; set; }
    [Required]
    public string Name { get; set; }

    public List<UserGenre> UserGenres { get; } = new();
}

public class UserGenre
{
    public int Id { get; set; }
    
    public string UserId { get; set; }
    public User User { get; set; } = null!;
    
    public int GenreId { get; set; }
    public Genre Genre { get; set; } = null!;
}

public class UserGenre
{
    public int Id { get; set; }
    
    public string UserId { get; set; }
    public User User { get; set; } = null!;
    
    public int GenreId { get; set; }
    public Genre Genre { get; set; } = null!;
}