The only way I could work it out was to put a number control in the repeating section

(set range validation to yes min 1 max 5, and data type integer.)

you could add a description or label to describe the numbers.

Then in a variable do a max function around the form.repeatingsection.intcontrol

Then I added the variable into a label outside the repeating section on the form.

It's not pretty but I couldn't see a way on the row by row to convert the text dropdown to an integer for use in the max function.