All the text fonts are located in the internal layouts of B4XPreferenceDialog, via the designer. for instance, for prefdialog.TYPE_TEXT they can changed in the layout: textitem, but the better way to change them is via code when you iterate over the list:
For i = 0 To prefdialog.PrefItems.Size - 1
Dim pi As B4XPrefItem = prefdialog.PrefItems.Get(i)
If pi.ItemType = prefdialog.TYPE_TEXT Then
Dim ft As B4XFloatTextField = prefdialog.CustomListView1.GetPanel(i).GetView(0).Tag
ft.TextField.Font = xui.CreateDefaultBoldFont(34) 'or whatever you want
'rest
end if
Next
By the way, when are you going to get rid of the mask