Qt how to create many windows inside one?

Question

Qt

How can I make a window within a window in a certain area so that it can be positioned, cascaded, gridded, and so on?

Answer 1

I myself have not worked with this under Qt, but this is called a "multi-document interface" and the simplest example is here.
doc.qt.io/qt-5/qtwidgets-mainwindows-mdi-example.html
You can also google "Qt MDI".