I used the less than range threshold and had no trouble getting the interrupt to work. When my hand was > 20 cm from the sensor, all output to the serial monotor would stop. When my hand got closer than 20 cm, the output would resume. Didn’t see any issue with the Pololu library; I think it is as complete as needs to be. The best is to just use the ST API, it is by definition the most complete. But good luck trying to understand it. It uses pointers to pointers and is written in the best spaghetti code fashion with few comments, redundant functions, mystery hex values and all kinds of confusion. Shameful, really, that ST treats its retail customers this way!
OK, I take it back, I used an if/then test in the loop not an interrupt to check for range.