How can I make this form responsive?

Question

Qt

I can’t understand at all why adaptability does not work in this form. If you need any more information, please contact.

Answer 1

Read any Qt book before you try to write code, save yourself many weeks of work.
QSizePolicy
PS But in general, looking at this design, I would like to recommend QML, QtWidgets have not been developed for a bunch of years.