Inheritance Cast

namespace InheritanceProblem
{
    public class IdentityUser {
        [Key]
        public required string Id { get; set; }
    
    }
    public class AppUser : IdentityUser {
        public required string Name { get; set; }
    }

    public class IdentityDbContext<TUser> : DbContext where TUser : IdentityUser
    {
        public IdentityDbContext(DbContextOptions options) : base(options) { }
        public DbSet<TUser> Users { get; set;}
    }

    public class AppDbContext : IdentityDbContext<AppUser>
    {
        public AppDbContext(DbContextOptions options) : base(options) { }
    }

    public class AppDbContextFactory : IDesignTimeDbContextFactory<AppDbContext>
    {
        public AppDbContext CreateDbContext(string[] args)
        {
            DbContextOptionsBuilder optionsBuilder = new DbContextOptionsBuilder();
            optionsBuilder.UseSqlServer("");
            return new AppDbContext(optionsBuilder.Options);
        }
    }

    public class SomeClass
    {
        public IdentityUser FindFirstUser(IdentityDbContext<IdentityUser> dbContext) => dbContext.Users.First();
    }

    public class Main
    {
        public Main()
        {
            SomeClass someClass = new SomeClass();
            AppDbContext context = new AppDbContextFactory().CreateDbContext(null);
            someClass.FindFirstUser(context);
        }
    }
}

namespace InheritanceProblem
{
    public class IdentityUser {
        [Key]
        public required string Id { get; set; }
    
    }
    public class AppUser : IdentityUser {
        public required string Name { get; set; }
    }

    public class IdentityDbContext<TUser> : DbContext where TUser : IdentityUser
    {
        public IdentityDbContext(DbContextOptions options) : base(options) { }
        public DbSet<TUser> Users { get; set;}
    }

    public class AppDbContext : IdentityDbContext<AppUser>
    {
        public AppDbContext(DbContextOptions options) : base(options) { }
    }

    public class AppDbContextFactory : IDesignTimeDbContextFactory<AppDbContext>
    {
        public AppDbContext CreateDbContext(string[] args)
        {
            DbContextOptionsBuilder optionsBuilder = new DbContextOptionsBuilder();
            optionsBuilder.UseSqlServer("");
            return new AppDbContext(optionsBuilder.Options);
        }
    }

    public class SomeClass
    {
        public IdentityUser FindFirstUser(IdentityDbContext<IdentityUser> dbContext) => dbContext.Users.First();
    }

    public class Main
    {
        public Main()
        {
            SomeClass someClass = new SomeClass();
            AppDbContext context = new AppDbContextFactory().CreateDbContext(null);
            someClass.FindFirstUser(context);
        }
    }
}