I have the same issue and would like to find the option to make the toolbar icons a bit larger.
Used to be a few years ago, before all these extra features were added, before the extra icons, that Scribus' toolbar icons were larger.
Most likely related to Scribus using Qt5.
Adobe Indesign does the same thing.
I want an option that I can choose which icons that I frequently use and can remain on the top of the program, and the rest be hidden.
LibreOffice/OpenOffice does this.