In Scribus, when we use Text Frame, it will choose one font by default. Sometimes, we need to change this default font. To do it, go to menu File > Preferences > Tools > Text Frame Properties > change the default font. In this example, we choose FreeSans Medium 12pt. So, every new frame in new document will have this font.
Note: additional options above such as Text Color can be adjusted for more specific needs. For example, select Text Color green if you want all text later to be green. Press Defaults button to reset any option you change to default.