@Joe-von-Habsburg said in Add ready widget into widget:

I am leaving an example

QtCreator Preferences is your example?!
So you want something similar?!

You could dig into QtCreator source code and check out how it's done.
For this I would use QToolButton to populate the "menu bar" on the left and a QStackedWidget to display the content pages on the right. Actually the QStackedWidget is more like centered, as the whole window you see is divided into two sections (~15% / ~85%) for the menu and the "rest" (the QStackedWidget for the content).

Is it Qt designer form class (.cpp && .h && .ui)?

The "right side" is the content widget... In case of QtCreator a custom QWidget containing a QTabWidget for the Text Editor settings among many other things.
The parent of all this is probably a QStackedWidget as I presumed above.

What approach (with or without Designer Form) you pick to implement this has nothing to do with how it works.
Both ways are possible.

@silvio

Show the code please.

Any chance that the ui file is not used at all or the project overwrites the ui file layout by setting a new one using the widget's code?!

dc4d228b-0604-4860-ba95-ae4541f57518-image.png

am having the same issue .
if I create a new project then select the Qt version 6 and then run the default code it produces no output .Ho do i fix fix this ?
On the other hand if i start a new project and select the target Qt as Qt5 , it runs and produces an output..
so what could be the issue
da7bf813-5f34-42ca-abfb-40fd17527ea9-image.png