A roof needs to breathe from soffit to ridge. Get it wrong and the deck cooks in summer and sweats in winter, and the shingles age from underneath where nobody looks.
Intake is usually the problem
Everyone adds ridge vent. Far fewer check that the soffits are open, and a ridge vent with no intake does very little.
Do not mix vent types
Ridge vent plus powered fans short-circuits the airflow, pulling from the ridge instead of the eaves.