Filling blank space or embedding while a window is resizing (Qt)

Question

Video, which is showing defference between resizing in GTK and Qt
How to make "smart resizing" using Qt Designer?

UI files:

• Qt UI file
• GTK Glade file

I prefer to use Qt Designer and Python 3 (PyQt5)

Answer 1

I added layout (Lay Out -> Lay Out Vertically). Thank @ekhumoro.