Looking for a solution in Survey 123 Connect.
I don't think there's a built-in way to do this. This is discussed in this thread:
How to format display of calculated result in Survey123
I have done this using a combination of string-length(), concat(), and substr(), however. I broke the number into sub-strings based on its length using "if" statements, and concatenated commas between the sub-strings. It's not clean, but it has worked for me.
Due to the hard-coding of sub-strings, this doesn't work with negative numbers (though it could if you made some modifications).
Attached are a few examples of integer inputs and the formatted text calculated.
Retrieving data ...