Hi,
I got the same issue using Scribus 1.5.2 on Win10 after double-clicking on the Scribus main window "top-bar".
For the attention of French people who may find that post, you have to use ALT+SPACE + "N" (from Agrandir).
Thanks for the trick, as the Win10 taskbar doesn't offer these options anymore, I was a bit lost too...