Hello Avery,
I agree with Joerg that the interrogation of the QT118H output may not need the use of an interrupt. However, here is a more general answer to your query -
For those MCUs where the KBI module does not provide polarity selection, another possible interrupt source that can be used is one of the timer input capture channels. This can be set up to trigger on either, or both edges of the input. In this case, the actual input capture value is not required, and can be ignored (apart from the flag clearing process).
Regards,
Mac