in layout tab, select conditional and use an expression, something like below. this example has almost all possible combinations of field values so modify to your needs.
the text box will show only if all the values are selected for the fields you specify, otherwise, it won't.
=if(GetFieldSelections(State)='(TX|MI)' and GetFieldSelections([FIPS County])='(12012|10000)' and GetFieldSelections(Region)='("Central North"|East)',1,0)
if you need just the field combinations, i would use the following expression in the conditional show:
getselectedcount(/*FieldName1*/)>0 and getselectedcount(/*FieldName2*/)>0
In the text object go in the "layout" tab, then in the "show" section select "conditional" and write:
=GetSelectedCount(myField) > 0
with this instruction you display the text box only if there is at least a selection in the specified field. (if you have more than one field to test add conditions with and
e.g: =GetSelectedCount(myField1) > 0 and GetSelectedCount(myField2) > 0