Hi,
if a field group has a description text the text only gets displayed on mouse hover in a tooltip. There is no (i) icon as for e.g. a single value form field.
I suggest to display the description text of a field group inline under its name - the same way as it is with data table field or as it can be handled for item lists. There are two checkboxes for "Show form field name" and "Show form field description". This would be great to have in the advanced configuration of a field group.
Kind regards,
Sébastien