Is there any way I can change the font size of the folder list on the
right?
I don't know of a "folder list on the right side". I know only of one in
the Navigation Pane on the left side. Do you mean the header columns or the
sender/subject list? View>Arrange By>Current View>Customize Current
View>Other Settings. The "Column Font" controls the column headers. The
"Row Font" controls the sender/subject/date entries.