TToolButton = class(Vcl.ComCtrls.TToolButton)
  strict private
    procedure CMVisibleChanged(var AMsg: TMessage); message CM_VISIBLECHANGED;
  end;

procedure TToolButton.CMVisibleChanged(var AMsg: TMessage);
const
  CSepStyles: set of TToolButtonStyle = [tbsSeparator, tbsDivider];
var
  Li: Integer;
  LBtn: Vcl.ComCtrls.TToolButton;
begin
  inherited;
  if (csDesigning in ComponentState) or (FToolBar = nil) or (Style in CSepStyles) then
    Exit;
  if not Visible then begin
    for Li := Index - 1 downto 0 do begin
      LBtn := FToolBar.Buttons[Li];
      if LBtn.Style in CSepStyles then
        Break;
      if LBtn.Visible then
        Exit;
    end;
  end;

  for Li := Index + 1 to FToolBar.ButtonCount - 1 do begin
    LBtn := FToolBar.Buttons[Li];
    if LBtn.Style in CSepStyles then begin
      LBtn.Visible := Visible;
      Exit;
    end;
    if LBtn.Visible then
      Exit;
  end;
end;