Clearing the memory occupied by class properties on form close?

Question

Delphi

Greetings.
I'm studying Delphi and came across such a problem: you need to clear the memory occupied by the properties of a class instance when the form is closed.
The implementation is as follows (names, of course, fictitious):

unit Unit1;

interface

uses Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms, Dialogs, StdCtrls, ExtCtrls, ExtDlgs, ComCtrls;

type
  TForm1 = class(TForm)
    ...
    procedure FormCreate(Sender: TObject);
    procedure FormClose(Sender: TObject; var Action: TCloseAction);
  end;

  MyClass = class
    St_L1, St_L2: TStringList;
    constructor Create();
  end;

  MainClass = class
    MyStrings: MyClass;
    ...
    procedure CreateMyClass();
  end;

var
  MC: MainClass;

implementation

{$R *.dfm}

constructor MyClass.Create();
begin
  St_L1 := TStringList.Create;
  St_L2 := TStringList.Create;
end;

destructor MyClass.Destroy();
begin
  St_L2 .Free;
  St_L2 .Free;
end;

procedure MainClass.CreateMyClass();
begin
  MyStrings := MyClass.Create();
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  MC.CreateMyClass();
end;

// ...

procedure TForm1.FormClose(Sender: TObject; var Action: TCloseAction);
begin
  MC.Destroy();
end;

end.

Does it make sense to write a destructor for MyClass at all , if I destroy the MC instance at the end => the memory occupied by two TStringList is cleared automatically in principle? If there are nit-picking about the implementation, then I ask them to be put on public display, as I am learning.
PS This implementation was chosen because I want to make calls to the properties and methods of my child classes through my main, "global" class (in this case, this is MainClass )
Thank you.
UPDATE continuation of the 4th question

type
    Books = class
        Title: String;
        Author: String;
        PublYear: Integer;
        constructor Create(Title: String; Author: String; PublYear: Integer);
    end;
    
    Library = class
        Book: array [1..100] of Books;
        Counter;
        constructor Create();
        procedure AddBook(T: String; A: String; PY: Integer);
        function GetBookTitle(N: Integer): String;
    end;

constructor Create(Title: String; Author: String; PublYear: Integer);
begin
    self.Title := Title;
    self.Author := Author;
    self.PublYear := PublYear;
end;

constructor Library.Create();
begin
    Counter := 0;
end;

procedure Library.AddBook(T: String; A: String; PY: Integer);
begin
    Counter := Counter + 1;
    Book[Counter] := Books.Create(T, A, PY);
end;

function GetBookTitle(N: Integer): String;
begin
    Result := Book[N].Title;
end;

var
    LB: Library;

begin

    LB := Library.Create();
    LB.AddBook('Утиные истории', 'Дональд Дак', 2999);

    ShowMessage(LB.GetBookTitle(1));

end.

Answer 1

1. MS - not initialized.
That is, it must appear somewhere else:
Otherwise, the behavior of the program is not predictable.
2. There will be no auto-deletion here. Unless you explicitly delete TStringLists, they will remain in memory (which is logical, because, for example, you could pass them to other objects). It follows that FList of type TStringItemList (which is essentially a dynamic array) and all the strings that are stored in them will remain in memory forever.
3. If you are wondering if your program has memory leaks, use
reportmemoryleaksonshutdown := true;
Google will tell you the details.
4. About the implementation with the global class - I didn't quite understand the technique, but it looks very controversial.
5. MC.Destroy - it's better to replace it with FreeAndNil(MC), but still, you need to write

TMainClass = class(TObject)
  ...
  destructor Destroy; override;
end;

...

destructor TMainClass.Destroy;
begin
  MyStrings.Free;
end;

6. It is better to transfer the creation of a subobject by the CreateMyClass procedure to the constructs of the "main class".