"Create" Action Method Not Working ASP.NET Core

When I add the following lines to the Tournament class the Create action method doesn't work in the webapp It just reloads the page. I recorded a short clip to show what it does: https://youtu.be/pvanpQD8LhM. I am using .NET 7

Code causing the problem:

        public ICollection<Game> Games { get; set; }

Here's the classes:

using System.ComponentModel.DataAnnotations;

namespace WebApplication3.Models
{
    public class Tournament
    {
     
        public int TournamentId { get; set; }
        [Required]
        public string TournamentName { get; set; }
        [Required]
        public string Location { get; set; }
        //public DateTime StartDate { get; set; }
        //public DateTime EndDate { get; set; }

        public ICollection<Game> Games { get; set; }
        
    }
}

namespace WebApplication3.Models
{
    public class Game
    {
        public int GameId { get; set; }
        //public DateTime GameDate { get; set; }
        public string Player1 { get; set; }
        public string Player2 { get; set; }
        public string Score { get; set; }

        public int TournamentId { get; set; }
        public Tournament Tournament { get; set; }
    }
}

I first tried different code from a Tutorial, which didn't work. I got this from the EFTutorial website. I have also tried removing the required annotations.

Edit:

Here's the create action method for Tournament:

 public IActionResult Create()
        {
            
            return View();
        }

        // POST: Tournament/Create
        // To protect from overposting attacks, enable the specific properties you want to bind to.
        // For more details, see http://go.microsoft.com/fwlink/?LinkId=317598.
        [HttpPost]
        [ValidateAntiForgeryToken]
        public async Task<IActionResult> Create([Bind("TournamentId,TournamentName,Location")] Tournament tournament)
        {
            if (ModelState.IsValid)
            {
                _context.Add(tournament);
                await _context.SaveChangesAsync();
                return RedirectToAction(nameof(Index));
            }
            return View(tournament);
        }

Here's the create action method for Game:

 public IActionResult Create()
        {
            ViewData["TournamentId"] = new SelectList(_context.Tournament, "TournamentId", "TournamentId");
            return View();
        }

        // POST: Game/Create
        // To protect from overposting attacks, enable the specific properties you want to bind to.
        // For more details, see http://go.microsoft.com/fwlink/?LinkId=317598.
        [HttpPost]
        [ValidateAntiForgeryToken]
        public async Task<IActionResult> Create([Bind("GameId,Player1,Player2,Score,TournamentId")] Game game)
        {
            if (ModelState.IsValid)
            {
                _context.Add(game);
                await _context.SaveChangesAsync();
                return RedirectToAction(nameof(Index));
            }
            ViewData["TournamentId"] = new SelectList(_context.Tournament, "TournamentId", "TournamentId", game.TournamentId);
            return View(game);
        }

@TJ_Frags you might want to try and just simply redirect to index in your create method. If that works then you need to debug your code from if (ModelState.IsValid) onwards. My guess is your RedirectToAction(nameof(Index)); is not reachable as public ICollection<Game> Games { get; set; } might be invalidating model state.

public IActionResult Create()
    {
        
        return View();
    }

    // POST: Tournament/Create
    // To protect from overposting attacks, enable the specific properties you want to bind to.
    // For more details, see http://go.microsoft.com/fwlink/?LinkId=317598.
    [HttpPost]
    [ValidateAntiForgeryToken]
    public async Task<IActionResult> Create([Bind("TournamentId,TournamentName,Location")] Tournament tournament)
    {
       
            return RedirectToAction(nameof(Index));
        
        
    }

From your description in this post, I think every time you create Tournament model in HttpPost create action, ModelState.IsValid is false and you will run return View(tournament) then the page will reload and show The Games field is required. error message in your view, right?

The reason is Beginning with .NET 6, new projects include the <Nullable>enable</Nullable> element in the project file. It means the project will add [requried] attribute by default even if you don't add it manually. So when you create Tournament model. The Games field is null, So ModelState.IsValid will be false and return The Games field is required. error message. You can just add ? to make this field nullable.

public ICollection<Game>? Games { get; set; }