Mocking repository method returns null instead expected value

public interface IUnitOfWork
{
   ICarRepository CarRepository { get; }
   ...
}

ICarRepository has (besides other methods) GetById(int id) method. 
That call I want to mock inside IUnitOfWork mock.

[Test]
public async Task Test()
{
    var unitOfWorkMock = new Mock<IUnitOfWork>();
   
    unitOfWorkMock.Setup(x => x.CarRepository.GetById(It.IsAny<int>()))
    .ReturnsAsync(new Car(){Name = "test"});
	
	var car = unitOfWork.Object.CarRepository.GetById(1); 
    //returns null

   var car2 = await unitOfWork.Object.CarRepository.GetById(1); 
    //returns null
	   	
	Any thoughts?
}

UPDATE:

public interface ICarRepository : IRepository<Car, int>
{
}

public interface IRepository<T, TId> where T : Entity<TId>
{
   Task<T?> GetById(TId id);
}
public class Car : Entity<int>
{   
}

I'm expecting that car should be populated with whatever I passed in Returns statement in the mock setup but instead I'm getting null.

This is not an actual answer; just a lengthy comment to report that this complete code:

public interface IUnitOfWork
{
    ICarRepository CarRepository { get; }
}
public interface ICarRepository : IRepository<Car, int>
{
}
public interface IRepository<T, TId> where T : Entity<TId>
{
    Task<T?> GetById(TId id);                                  // question mark on T? is allowed; T is a reference type; nullable reference types are enabled
}
public class Car : Entity<int>
{
    internal string? Name { get; init; }
}
public class Entity<T>
{
}

public class F
{
    [Test]
    public async Task Test()
    {
        var unitOfWorkMock = new Mock<IUnitOfWork>();          // also works: new Mock<IUnitOfWork>(MockBehavior.Strict)

        unitOfWorkMock.Setup(x => x.CarRepository.GetById(It.IsAny<int>()))
            .ReturnsAsync(new Car { Name = "test", });

        Car? car2 = await unitOfWorkMock.Object.CarRepository.GetById(1);

        // car2 is nonnull and instance has 'Name' equal to "test"
    }
}

together with Moq version 4.18.4, does not reproduce the problem. car2 is as expected at the bottom of Test().

So the asker must supply more details in the question. Try to prepare a complete reproduction code (with no types implicit).