It doesn’t really work like that because of the lifecycle of HIV.

If someone is using PrEP and is exposed to HIV, then either the drug works and they avoid infection (in which case there is obviously no impact on drug resistance) or they become HIV+. But in that case, they were either exposed to an already-resistant variant, or they were astonishingly unlucky and the drug failed to prevent infection - in which case, resistance is a moot point.

A person needs to develop an active HIV infection in order to communicate the disease to another. PrEP prevents this from happening in the first place.