Filtering a report for Combined Text Summary Field

If you want a non generic answer to your specific question, you can make a formula checkbox field called [Multiple Fruits?] with a formula of

Part(ToText([Fruit Salad]),2, ";") <> "" 

That formula says is look at the [Fruit Salad] combined text summary field, convert it to a text string which will be semicolon delimited and then look at the second part of that string which is delimited by a semicolon and see if it is blank. If it's not equal to blank that means there was a second part and that means there's least two fruits in the salad.

If you wanted a more generic solution then you could create a formula numeric field called [# of Fruits] and Filter the report where the # of Fruits is >= 2.

var text value = ToText([Fruit Salad]);

Count(
Trim(Part($value,1,";"))<>"",
Trim(Part($value,2,";"))<>"",
Trim(Part($value,3,";"))<>"",
Trim(Part($value,4,";"))<>"",
Trim(Part($value,5,";"))<>"",
Trim(Part($value,6,";"))<>"",
Trim(Part($value,7,";"))<>"",
Trim(Part($value,8,";"))<>"",
Trim(Part($value,9,";"))<>"",
Trim(Part($value,10,";"))<>"",
Trim(Part($value,11,";"))<>"",
Trim(Part($value,12,";"))<>"",
Trim(Part($value,13,";"))<>"",
Trim(Part($value,14,";"))<>"",
Trim(Part($value,15,";"))<>"",
Trim(Part($value,16,";"))<>"",
Trim(Part($value,17,";"))<>"",
Trim(Part($value,18,";"))<>"",
Trim(Part($value,19,";"))<>"",
Trim(Part($value,20,";"))<>"",
Trim(Part($value,21,";"))<>"",
Trim(Part($value,22,";"))<>"",
Trim(Part($value,23,";"))<>"",
Trim(Part($value,24,";"))<>"",
Trim(Part($value,25,";"))<>"")