It is entirely possible to create PySide6 applications without relying on .ui files or Qt Designer. Developers can construct all GUI elements, including windows, buttons, and labels, directly within Python code. This approach offers greater control and keeps all interface logic consolidated. A basic PySide6 application requires a QApplication instance and a QWidget to display. Widgets can be created and parented to a window, but without layouts, they occupy fixed positions. Qt layouts like QVBoxLayout, QHBoxLayout, and QGridLayout are essential for automatically arranging widgets. To manage complexity, it's recommended to subclass QWidget or QMainWindow. Signals and slots enable interactivity; for instance, a button's 'clicked' signal can be connected to a Python function. QMainWindow provides a framework for menus, toolbars, and status bars, with content placed in a central widget. Nested layouts can be achieved by adding one layout to another using addLayout(). The demonstration culminates in a complete QMainWindow application, showcasing programmatic GUI creation with interactive elements and a status bar.