Delphi FMX project going into the background

Question

How can my Delphi 10.4.2 project detect that it is going into the background?

I've tried using TMainWindow.FormDeactivate() but this leaves the floating tool window staying on top of all other application windows as the project goes into the background.

To solve that I've also tried...

procedure TMainWindow.FormDeactivate(Sender: TObject);
begin
  FloatingToolWindow.FormStyle := TFormStyle.Normal;
end;

...but this does not always work. For example, if the floating tool window has the focus (rather than the main window), then the main window's FormDeactivate() does not get called when the user clicks in another application - which leaves the tool window floating over all other application windows.

Here is a project that duplicates the problem. Run the project in Windows or in MacOS, click the button to show the tool window, click in the tool window (to give it focus), and finally click some other application's window to put this project in the background. The tool window continues to stay on top and the main window's FormDeactivate() is not called.

unit MainForm;

interface

uses
  System.SysUtils, System.Types, System.UITypes, System.Classes, System.Variants,
  FMX.Types, FMX.Controls, FMX.Forms, FMX.Graphics, FMX.Dialogs,
  FMX.Controls.Presentation, FMX.StdCtrls;

type
  TMainWindow = class(TForm)
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
    procedure FormDeactivate(Sender: TObject);
    procedure FormActivate(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  MainWindow: TMainWindow;

implementation

{$R *.fmx}

uses FloatingForm;

procedure TMainWindow.Button1Click(Sender: TObject);
begin
  FloatingToolWindow.Show;
end;



procedure TMainWindow.FormActivate(Sender: TObject);
begin
  FloatingToolWindow.FormStyle := TFormStyle.StayOnTop;
end;



procedure TMainWindow.FormDeactivate(Sender: TObject);
begin
  FloatingToolWindow.FormStyle := TFormStyle.Normal;
end;



end.

The main form's DFM:

object MainWindow: TMainWindow
  Left = 0
  Top = 0
  Caption = 'Form1'
  ClientHeight = 480
  ClientWidth = 640
  FormFactor.Width = 320
  FormFactor.Height = 480
  FormFactor.Devices = [Desktop]
  OnActivate = FormActivate
  OnDeactivate = FormDeactivate
  DesignerMasterStyle = 0
  object Button1: TButton
    Position.X = 280.000000000000000000
    Position.Y = 232.000000000000000000
    Size.Width = 137.000000000000000000
    Size.Height = 22.000000000000000000
    Size.PlatformDefault = False
    TabOrder = 0
    Text = 'Show Floater'
    OnClick = Button1Click
  end
end

The settings for the floating form:

object FloatingToolWindow: TFloatingToolWindow
  Left = 0
  Top = 0
  BorderIcons = []
  BorderStyle = ToolWindow
  Caption = 'Form2'
  ClientHeight = 316
  ClientWidth = 491
  FormStyle = StayOnTop
  FormFactor.Width = 320
  FormFactor.Height = 480
  FormFactor.Devices = [Desktop]
  DesignerMasterStyle = 0
  object Text1: TText
    Position.X = 80.000000000000000000
    Position.Y = 88.000000000000000000
    Size.Width = 297.000000000000000000
    Size.Height = 113.000000000000000000
    Size.PlatformDefault = False
    Text = 
      'Click on this tool window (to give it focus) and then click on a' +
      'ny OTHER application'#39's window to send this project into the back' +
      'ground. This window will continue to stay on top of the other ap' +
      'plications.'
  end
end

Source for the tool window:

unit FloatingForm;

interface

uses
  System.SysUtils, System.Types, System.UITypes, System.Classes, System.Variants,
  FMX.Types, FMX.Controls, FMX.Forms, FMX.Graphics, FMX.Dialogs,
  FMX.Controls.Presentation, FMX.StdCtrls, FMX.Objects;

type
  TFloatingToolWindow = class(TForm)
    Text1: TText;
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  FloatingToolWindow: TFloatingToolWindow;

implementation

{$R *.fmx}

end.