2017 Prius AC not blowing cold when car is still?

Back in the engine-driven compressor days this could be a sign of a slipping belt or weak tensioner. Or a leak in the system and low freon charge. Present day systems are all electric and computer controlled, which makes DIY diagnosis more difficult. If you've already checked the obvious things like a clean HVAC filter, no obvious damage under the hood, and proper control panel settings, my next step would be toward the dealer service department. Feel free to tinker, but the HVAC system in these vehicles is high tech and expensive.

 

First thing I'd check would be the cooling fans that pull air through the A/C condenser out front. Don't need them when the car is moving because the car's airspeed does the job.