zegtern Almost everything is an object, your player is a node, so is an object. According to the posted flow diagram, you may be benefit of using PackedScene to store your player node (or even the current played scene?). All relies on "what you want to save?"

      zegtern Essentially:

      var my_node = get_node("foo") # <- First, get a reference of the node you want to save
var packed_scene = PackedScene.new() # <- Create a new PackedScene resource where your node will be stored

packed_scene.pack(my_node) # Now store your node in the resource.
# Keep in mind that it'll save your node and all subnodes that uses it as owner. Other nodes are discarded.

var error = ResourceSaver.save(packed_scene, "user://path/to/your/file.scn") # Save your resource as file

assert(error == OK) # Verify that everything went OK when saving the resource. If something went wrong, the program will halt here.

      You can see more about it here: https://docs.godotengine.org/en/stable/classes/class_packedscene.html#class-packedscene-method-pack

      Also, here's a good guide about saving things using File class: https://kidscancode.org/godot_recipes/3.x/basics/file_io/

          Please see the code below.
          If you save a player in this code, the tempInt value is also saved, and the next time you load the saved player, the saved tempInt value is the initial 0 value, not the abnormally stored value.

          //[Player.cs]
public partial class Player : Resource
{
    public int tempInt { get; set; } = 0;

}
          //Main.cs
public partial class Main : Node
{
    public Player player;

    public override void _Ready()
    {
        base._Ready();
        player = new Player();
        player.tempInt = 0;
    }

    public override void _Input(InputEvent inputEvent)
    {
        if (inputEvent is InputEventKey keyEvent && keyEvent.Pressed)
            switch (keyEvent.Keycode)
            {
                case Key.A:
                    player.tempInt++;
                    GD.Print(player.tempInt);
                    break;


                case Key.S:
                    var fooPath = System.Environment.CurrentDirectory + "\\" + "Save";
                    if (Directory.Exists(fooPath) == false)
                    {
                        Directory.CreateDirectory(fooPath);
                    }

                    GD.Print(player.tempInt);
                    
                    ResourceSaver.Save(player, fooPath + "\\player.tres");
                    break;

                case Key.L:
                    var loadPath = System.Environment.CurrentDirectory + "\\"+ "Save";
                    
                    player = (Player) ResourceLoader.Load(loadPath+ "\\player.tres");
                    
                    GD.Print(player.tempInt);

                    break;

            }
    }

}

          AnidemDex Please see the code below.
          If you save a player in this code, the tempInt value is also saved, and the next time you load the saved player, the saved tempInt value is the initial 0 value, not the abnormally stored value.

          //[Player.cs]
          public partial class Player : Resource
          {
          public int tempInt { get; set; } = 0;

          }

          //Main.cs
          public partial class Main : Node
          {
          public Player player;

          public override void _Ready()
{
    base._Ready();
    player = new Player();
    player.tempInt = 0;
}

public override void _Input(InputEvent inputEvent)
{
    if (inputEvent is InputEventKey keyEvent && keyEvent.Pressed)
        switch (keyEvent.Keycode)
        {
            case Key.A:
                player.tempInt++;
                GD.Print(player.tempInt);
                break;


            case Key.S:
                var fooPath = System.Environment.CurrentDirectory + "\\" + "Save";
                if (Directory.Exists(fooPath) == false)
                {
                    Directory.CreateDirectory(fooPath);
                }

                GD.Print(player.tempInt);
                
                ResourceSaver.Save(player, fooPath + "\\player.tres");
                break;

            case Key.L:
                var loadPath = System.Environment.CurrentDirectory + "\\"+ "Save";
                
                player = (Player) ResourceLoader.Load(loadPath+ "\\player.tres");
                
                GD.Print(player.tempInt);

                break;

        }
}

          }

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