The issue with using a cover while stored outside, even with a breathable cover, is the morning dew on the hood, roof and trunk lid. Especially the roof. Because of temperature change throughout the day, dew will form, usually in the morning as temps rise a bit. So you now have moisture on your roof and the cover lying directly on it. The cover will soak up a bit of moisture and the process of evaporation is slowed. This is especially a problem is a car is left in prime. Prime is porous. Moisture, especially morning dew goes right through the primer onto the metal. Rust then starts from the bottom and works its way to the surface. Usually showing itself after the car has been painted. As for the heat of the summer, a cover can leave an imprint on the flat surfaces of the car that have been baked. I've seen that several times and the paint damage is not easy to fix.
My opinion is, that if you have to leave it outside, spring for a cheap tent. Maybe something like this. https://www.menards.com/main/building-materials/carports-shelters/fabric-carports-shelters/shelterlogic-max-all-purpose-10-x-20-canopy-6-leg-white/31757/p-1444441927798-c-10153.htm?tid=6899415671622133052&ipos=1