Hey guys and sorry for the belated reply.

Your example looks good. Thank you for that!
Also, I did find out how to use SpacerItems as stretch items. I always forgot to change the QSizePolicy, so nothing could stretch. Now, after removing fixed sizes and giving each column diffent stretch factors, I can handle correct grid positioning with expanding spacers.

Maybe one last question:
After having removed all fix widths/heights, each edit in my gui has a predefined maximal and a predefined minimal width. But, not every edit is displayed with the same width when I run the program.
Instead, some edits are shown with a smaller width and when I enlarge the window, they grow to the maximum width like the other edits have it from the beginning.

Is there a way to set fixed "starting widths" for every edit?

Kind regards,
Binary