Can't change font style?

That looks like the pop-up quick toolbar that appears over the selected area. There should be a "Tool Options" tab in one of the floating toolboxes (mine is on the bottom-left side of the screen by default) that has additional options when the Text tool is selected. If it's not there you can add it to a toolbox through the little left-pointing triangle on the tab bar.

In this on-canvas dialog, you choose a font by typing the first (few) letters of its name (in the entry that displays 'Sans' in the screenshot). Then, a selection of matching fonts pops up.